Agricultural Ecosystems Program: Understanding Sources and Sinks of Nutrients and Sediment in the Upper Susquehanna River Basin

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Agricultural Ecosystems Program: Understanding Sources and Sinks of Nutrients and Sediment in the Upper Susquehanna River Basin
Project Description.
Objectives:

Our goal is to gain a better understanding of the sources and sinks of nitrogen (N), phosphorus (P), and sediment in a large rural watershed of mixed land use, including agricultural and forest lands. The geographic focus is the Susquehanna River drainage basin and its tributaries within New York State (an area of approximately 19,500 km²), with an emphasis on N and P dynamics of the agricultural and forested landscapes of the region. The Susquehanna is the largest river east of the Mississippi in the US, the largest tributary of Chesapeake Bay, and the single largest source of nutrients to the main stem of the Bay. Thus, better understanding the sources and sinks of nutrients and sediment in the Susquehanna can lead towards better management of nutrient fluxes from the landscape and thus water quality in Chesapeake Bay. The proposed research will also lead to a better understanding of the controls on nutrient pollution – particularly N pollution – in rural landscapes in general, and to insights on sustaining agriculture in the northeastern US in a manner that best harmonizes with environmental quality. A major sub theme will be how climate variability and climate change influence the fluxes of N, P, and sediments from the rural landscape. N is the primary focus, both because it is the primary pollution problem in coastal systems such as Chesapeake Bay, and because sources and sinks are more poorly understood than for P. Nonetheless, much can be gained from simultaneous study of the dynamics of N, P, and sediments.

Progress Report: This will be a new project.
Justification and Literature Review:

The human acceleration of the N cycle is one of the most pronounced aspects of global change, with the rate of increase in the formation of reactive N far exceeding the rate of accumulation of CO₂ in the atmosphere (Vitousek et al. 1997). The increased supply of N is a serious threat to the ecological functioning of a variety of ecosystems, including forests, streams, and lakes in addition to coastal marine ecosystems (Vitousek et al. 1997). However, coastal marine ecosystems are particularly at risk from N pollution, and N is now the largest pollution problem in the coastal waters of the U.S. (Nixon 1995; NRC 2000; Howarth et al. 2000; Rabalais 2002). N pollution also poses significant risks to human health in a variety of ways, including contamination of groundwater and drinking water and reduction in rural and urban air quality (Townsend et al. 2003).

N pollution in coastal systems has grown over the past few decades (NRC 2000; Howarth et al. 2000). The resulting eutrophication lowers biotic diversity, leads to hypoxic and anoxic conditions, increases the incidence and duration of harmful algal blooms, degrades the habitat quality of seagrass beds or even completely destroys them, and can lead to changes in ecological food webs that lower fishery production (NRC 2000). The National Coastal Condition Report (EPA 2001) lists eutrophic condition as one of the three greatest threats to the health of the nation’s estuaries, along with poor benthic condition (itself due to eutrophication, in part) and wetland loss. Some 40% of the estuarine area in the conterminous U.S. is severely degraded from eutrophication, and 67% is degraded to some extent (Bricker et al. 1999; EPA 2001). In the northeastern US, some 60% of estuarine area shows a high expression of eutrophic condition (EPA 2001). Both a “white-paper panel” of the Ecological Society of America (Vitousek et al. 1997) and the Coastal Marine Team of the National Climate Change Assessment (Boesch et al. 2000; Scavia et al. 2002) concluded that N pollution is one of the greatest consequences of human accelerated global change on the coastal oceans of the world. The societal implications are immense, as estuaries are among the most valuable of all ecosystems with regard to the services they provide (Costanza et al. 1997).
Only recently has a national consensus of water quality managers evolved that N rather than P is the prime cause of eutrophication in coastal marine ecosystems (NRC 2000; Howarth and Marino, in press). In sharp contrast, P is the leading cause of eutrophication in lakes, and P control has been the prime focus of water quality management in the U.S. for most of the past 3 decades. This focus on P led to much more research on sources and sinks of P in the landscape, and means to reduce inputs to surface waters. The knowledge base on sources of N is more limited, and more recent. Compared to P, N is much more mobile in the environment, with significant fluxes both through groundwater and atmospheric pathways. N also has significant biological sources and sinks through the microbial processes of N fixation and denitrification, adding to the complexity of the N cycle. This complexity poses significant challenges for understanding the sources of N pollution (NRC 2000; Howarth et al. 2002b). However, P can also contribute to degradation of water quality in coastal systems, and there is great value in studying the cycles of N and P in consort (NRC 2000; Howarth and Marino, in press).
The distribution of reactive N is far from uniform across the planet, and N pollution in coastal waters is greatest where agricultural activity and urbanization and air pollution are greatest. In some regions such as the North Sea and Yellow Sea, human activity probably has increased N fluxes to the coast by 10- to 15-fold or more, while in other areas such as Hudson’s Bay and Labrador, human activity probably has had little effect on N fluxes (Howarth 2003). On average for the US, human activity has increased N fluxes to the coast by an estimated 6-fold (Howarth et al. 2002a; Howarth 2003). Currently, the greatest increase in N pollution is occurring in Asia, particularly in China (Galloway et al. 2004). The increase in N inputs to coastal waters in the US was particularly dramatic in the 1960s and 1970s; since then, the rate of increase has slowed, yet N inputs to coastal waters in the US have continued to increase on average by ~1% per year over the past 15 years (Howarth et al. 2002a).
The single largest driver globally in acceleration of N cycling is the increased use of synthetic N fertilizer in agriculture, and half of the synthetic fertilizer that has ever been used on Earth has been applied in the past 15 years or so (Howarth et al. 2002b; Galloway et al. 2004). The combustion of fossil fuel also inadvertently creates reactive N. While globally the creation of reactive N from burning fossil fuels amounts to only 25% of the rate of N fertilizer synthesis (Galloway et al. 2004), in the US the atmospheric emissions and deposition of N from fossil fuel are relatively more important, at ~ 60% of the rate of use of synthetic N fertilizer (Howarth et al. 2002a). In many watersheds in the northeastern US, atmospheric deposition of N that originates from fossil fuel sources is a greater source of N than is fertilizer use (Boyer et al. 2002). Often, there is considerable uncertainty in the relative magnitudes of N sources in particular watersheds (NRC 2000). For example, for the watersheds of Chesapeake Bay including the Susquehanna, studies differ as to whether agricultural sources or atmospheric deposition onto the landscape are more important contributors of N (Magnien et al. 1995; Jaworski et al. 1997; NRC 2000; Boyer et al. 2002; Howarth et al. 2002b). Recent evidence suggests that the actual magnitude of atmospheric deposition onto the watersheds of Chesapeake Bay may have been underestimated severely in the past due to lack of consideration of high deposition near emission sources (Howarth et al., in press).
The uncertainty over the importance of atmospheric N deposition as a source of N pollution to surface waters stems from two issues: 1) the extent of dry deposition of N onto the landscape; and 2) the fate of the N that is deposited onto the landscape. The vast majority of measurements of N deposition – including those of the National Atmospheric Deposition Program (NADP) -- measure only wet deposition (N in rainfall and snow) or bulk deposition (wet deposition plus N deposited in open buckets during dry weather periods). Measurements of bulk deposition can substantially underestimate dry deposition and hence total N deposition, the sum of wet plus dry deposition (Lovett et al. 2000). Often, dry deposition (which includes aerosols and other particles and uptake of gaseous forms of N by vegetation, soils, and surface waters) is assumed to roughly equal rates of wet N deposition, but this assumption has a very limited data base to support it (Holland et al. 1999; Howarth et al. 2002b). Dry deposition is routinely measured in the US only at the limited number of sites that are part of the CASTNet and AIRMon-Dry programs. For N, not all of the components of gaseous dry deposition are measured (for example, NH₃ and NO₂ are not measured). Further, all of the CASTNet and AIRMon-Dry sites are deliberately chosen to estimate background levels of deposition and as such are located well away from emission sources. However, recent evidence suggests that dry deposition, particularly of gaseous N species, may often be substantially higher near emission sources, both for oxidized N gases and for ammonia (Fahey et al. 1999; Lovett et al. 2000; Cape et al. 2004; Howarth et al., in press).
Also highly uncertain is the fate of N that is deposited onto the landscape. Many models assume that N is tightly retained in forests (Magnien et al. 1995). However, recent syntheses of the effects of N deposition on temperate forests indicate that stream nitrate export often increases sharply as deposition increases above a threshold of approximately 8 to 10 kg N ha^-1 y^-1 (NRC 2000; Howarth et al. 2002b; Aber et al. 2003). This threshold effect is critical for understanding the fate of N in the upper Susquehanna River Basin, since this area receives some of the highest rates of N deposition in the country. Total (wet + dry) inorganic N deposition in the Upper Susquehanna Basin exceeds 10 kg N ha^-1 y^-1, or more than ten times pre-industrial background conditions (Holland et al. 1999). However, variability in stream N export increases with N loading as well: that is, some, but not all watersheds increase N export with elevated N inputs. Variability among watersheds receiving similar rates of N deposition can be quite large, with stream inorganic N exports ranging from 2% to 50% of inputs (Aber et al. 2003). Factors driving variation among watersheds may include differences in tree species composition (Lovett et al. 2000), past land-use history and stand age (Goodale et al. 2000), and variation in hydrologic flowpaths across watersheds or through time (Creed & Band 1998; Burns & Kendall 2002). Retention of N in soils and vegetation is expected to be greatest in old-field sites reverting to forest, with rates of N accumulation decreasing as stands age (Aber et al. 1998, 2003).
The contribution of N and P to surface waters from agricultural sources is highly dependent on a variety of management practices, including cropping systems and amount and timing of fertilizer application, as well as on soil type and climate (NRC 1993; Randall et al. 1997; Randall and Mulla 2001; Sogbedji et al. 2000, 2001; van Es et al. 2002; Howarth et al. 2002b; Kahabka et al., 2004). On average for the US, about 20% of the fertilizer N inputs to agricultural fields leach to surface or ground waters (NRC 1993; Howarth et al. 2002a). The variability among fields is great, though, ranging from a low for leaching loss of 3% for grasslands with clay-loam soils to 80% for some row-crop agricultural fields on sandy soils (Howarth et al. 1996). These results provide the opportunity to directly investigate management strategies to reduce off-site effects. The choice of cropping system is particularly important for influencing nutrient loss; for example, fields planted to perennial alfalfa lost 30- to 50-fold less nitrate than did fields planted in corn and soybeans in Minnesota and Iowa (Randall et al. 1997; Randall and Mulla 2001). Planting of winter cover crops can also be important for reducing nutrient losses; an experimental study in Maryland showed the long term effect of winter cover-crop plantings was a 3-fold reduction in nitrate loss (Staver and Brinsfield 1998). Interestingly, while no-till agriculture significantly reduces sediment and P losses from fields by reducing erosion, it has little if any effect on N losses (Randall and Mulla 2001). In fact, reduced tillage may also increase N leaching through the preservation of pore continuity that enhances drainage (Andreini and Steenhuis, 1990). Organic N from manure and converted sods is often introduced at a time (i.e., autumn) when little plant uptake occurs and as such the leaching losses are high (Sogbedji et al. 2000, 2001; van Es et al. 2002). Also, farmers typically ignore the seasonal variations in crop N needs due to weather conditions. Randall and Mulla (2001) demonstrated in Minnesota that fall application of fertilizer resulted in 305 to 40% greater N losses from fields over the year compared with spring or summer application. Similarly, fall application of manure results in high nitrate leaching losses on many dairy farms in New York (van Es et al., 2002) and also results in higher N fertilizer rates ( Howarth et al. 2002a).
Annual weather variability additionally contributes to inefficient N use on farms. Seasonal N needs are strongly influenced by weather conditions in that optimum fertilizer rates are higher in years with wet springs due to rapid leaching and dentrification (Sogbedji et al., 2001). Conversely, optimum N rates are considerable lower in dry years, but farmers still fertilize for the highest N demand, contributing to excessive (“insurance”) applications. This is especially critical because high residual N in dryer years poses the greatest concern for water contamination (McIsaac et al., 2001). It is believed that substantial reduction in environmental N losses may be achieved through more precise N management on farms.

The intensification of animal production systems, with major importation of feeds into a region, also contributes greatly to surface water pollution of P and N (NRC 2000; Howarth et al. 2002a, 2002b). A study of four northeast dairy farms by Klausner et al. (1998) showed approximately two-thirds of the N and phosphorous imported onto the farms was retained on a dairy farm or was unaccounted for while only a third was exported as milk, meat or crops. Many of the farm imports of N and P are animal feeds which are subsequently excreted as manure and land applied in excess of crop requirements. This can lead to direct nutrient losses to surface and groundwater as well as indirect losses when nutrients such as P accumulate and cause increasingly high fertility levels. Nitrate tests from wells on corn fields at Cornell’s Teaching and Research Center in Harford, NY, a dairy farm with 360 cows, increased from 3.3 to 7.0 mg kg^-1 over a 15-year period when feed imports increased 40%. During the same period on the same fields, soil P levels increased 4-fold to 24 kg ha^-1 (Wang et al. 1999). In New York State, currently 47% of the soils test above the agronomic optimum for P compared to 26% in the early 1980s (Ketterings et al., 2005). Further, ammonia volatilization from animal wastes can distribute N across the landscape, and may be a major contributor to N pollution in surface waters (NRC 2000; Howarth et al. 2002b). Fahey et al. (1999) demonstrated that across Tompkins County, NY (the home of Cornell University, and a landscape that is very close to and very similar to most of the upper Susquehanna River Basin) atmospheric deposition of ammonia/ammonium varied greatly in space, and was presumably much higher near agricultural sources.

Climate variability and climate change are likely to have a profound effect on the movement from the landscape and delivery of nutrients in rivers to coastal marine ecosystems, but there is great uncertainty as to the detailed responses expected (Boesch et al. 2000; Scavia et al. 2002). This uncertainty results in part from divergent predictions for future climate change, for example with some global models predicting a drier climate and some a wetter climate in the northeastern US as atmospheric carbon dioxide levels continue to rise over the next century (Wolock and McCabe 1999). Further uncertainty results from the non linearity in response of riverine freshwater discharge to changes in climate, with some models suggesting discharge will increase disproportionately to increases in precipitation, and others suggesting increases in discharge will be less than increases in precipitation (Najjar 1999; Wolock and McCabe 1999; Najjar et al. 2000). Beyond these uncertainties in the physical climate system and the hydrologic responses of watersheds, the biogeochemical responses to changes in climate and hydrology are difficult to predict, particularly for N.
Watersheds with greater precipitation and discharge will tend to have higher erosion rates, and this leads to higher fluxes of sediment and P from the landscape since most of the P in large rivers is particle bound (Moore et al. 1997; Howarth et al. 1995, 2002b).

N moves through the landscape primarily in dissolved forms, and N fluxes seem to be primarily controlled by the balance of sources and sinks of N in the landscape. For disturbed landscapes in the temperate zone, an average of 20 to 25% of the N inputs resulting from human activity is exported in rivers (Howarth et al. 1996, 2002b; Boyer et al. 2002). However, there is a pronounced climatic overlay on this. For the Mississippi River basin, McIsaac et al. (2001) demonstrated that during dry years, N accumulates in the soil or groundwater, and during wet years, this stored N is flushed out. There also is a steady-state influence of climate on N fluxes in rivers. In a comparative analysis of 16 large watersheds, Howarth et al. (in press) showed that the long-term, average fraction of human N inputs exported from the landscape downstream varied from as little as 10% in watersheds with relatively low precipitation and freshwater discharge to 40% or greater in watersheds with higher precipitation and higher discharge. Presumably, this reflects a greater loss of N from denitrification in the watersheds with lower precipitation and discharge. While this may seem paradoxical since denitrification is favored by waterlogged soils, the over-riding control may be water residence time (Seitzinger et al. 2002). In the watersheds with more precipitation and greater discharge, water may flow through zones of potentially high activity, such as riparian wetlands and first-order streams too quickly for significant denitrification to occur (Howarth et al., in press).

Conversely, N use is contributing significantly to climate change. Nitrous oxide (N₂O) is a greenhouse gas and is also detrimental to the ozone layer (Vitousek et al. 1997). Although the gas is emitted in much lower quantities than CO₂, it is 310-fold more effective as a greenhouse gas (per mass), and N₂O is responsible for 7.5 per cent of the calculated greenhouse effect caused by human activity (IPCC 2001). The concentration in the atmosphere is increasing at a rate of about 0.2 per cent per year. Agricultural soils are thought to be the major source of atmospheric N₂O at the global scale globally. All forms of N fertilizer can lead to N₂O emissions, and timing and rates of application are important modulating factors (Tan et al. 2005), and need to be considered concomitantly with water quality concerns.
Our proposed research program is designed to gain a better understanding of the sources of N and P flux within and from the upper Susquehanna River basin, an area that typifies much of the rural northeastern US and is also a direct contributor of N, P, and sediment to Chesapeake Bay. A federal interagency research plan for nutrient pollution developed in 2003 by NOAA, USDA, EPA, and NSF identifies the sort of research we propose here on better source characterization as one of the top national research priorities (Howarth et al. 2003). The proposed research should lead towards a better understanding of direct relevance to sustaining agriculture in the northeastern US in a manner that best harmonizes with environmental quality. We will specifically evaluate the importance of agricultural sources of nutrient pollution in the context of all sources in the watershed. The Cornell community has broad expertise in the disciplines required to achieve the goals. The proposed program is designed to foster creative new research and integrate the results with current research at Cornell into an overall, comprehensive effort that can have an impact larger than the sum of its parts.
The Upper Susquehanna River Basin study region:

The proposed work will focus on understanding the sources and sinks of N, P, and sediment in the drainage basin of the Susquehanna River and its tributaries within New York State (an area of ~ 19,500 km²), with an emphasis on N. The Susquehanna is the largest river east of the Mississippi in the US, the largest tributary to Chesapeake Bay, and the single largest source of nutrients to the main stem of the Bay (Hagy et al. 2004; Chesapeake Executive Council 2004). Chesapeake Bay, in turn, is the largest estuary in the US, and one of the most sensitive to the adverse effects of N pollution (NRC 2000). Approximately 25% of the entire Susquehanna River basin is in New York State.

Over the past few decades, N inputs to Chesapeake Bay have severely degraded water quality, with increasing volumes of oxygen-free waters devoid of fish life and the dieback of critical seagrass-bed habitat. In the 1980s, Maryland, Virginia, and Pennsylvania together with the US EPA agreed to reduce the inputs of N from controllable sources to the Chesapeake by 40% (Chesapeake Executive Council 1983, 1987). Despite significant efforts in these states, however, N inputs remain high, and water quality has improved little if at all (NRC 2000). As a result, the Chesapeake Bay Program (run by the US EPA), the Chesapeake Bay Commission, and the 6 states in the watershed of Chesapeake Bay have committed to further, stringent reductions in N, P, and sediment to the Bay (Chesapeake Executive Council 2000, 2004). Governor Pataki formally committed New York State to this goal in March of 2004. The proposed cap for N fluxes from New York State down the Susquehanna (to be reached by 2010) is 5,700 metric tons per year, which is a 26% reduction according to the estimates of the Chesapeake Bay model (Chesapeake Executive Council 2004). However, there is significant uncertainty in the current flux, as models differ in their estimation of the magnitude and routine monitoring has only begun in the past year. Also, climate variability and future climate change may tend to increase N fluxes in the Susquehanna, making it more difficult to reach the targeted reductions (Howarth et al., in press). Failure to meet this goal is likely to result in mandatory N and P reductions imposed by the EPA (Chesapeake Executive Council 2004).
The national importance of Chesapeake Bay, and the importance to the continued viability of New York State agriculture to meet the 2010 nutrient caps, provide strong justifications for the research we propose. More broadly, we view the upper Susquehanna River basin as an ideal “laboratory” for better understanding the factors that control N fluxes from rural landscapes with mixed agriculture and forest lands. The land use in the Susquehanna River basin is overwhelmingly rural, and the landscape is an interacting mixture of farmland (29% of the area) and forests (67% of the area; Boyer et al. 2002). The majority of this forest land was once in agriculture, and approximately 5% is in recently abandoned farmland reverting to forest (Laba et al. 2002). The rate of atmospheric deposition of oxidized N (NOy, which in this region originates largely from fossil fuel combustion) onto this landscape is amongst the highest in any rural area in the US (Holland et al. 1999; Boyer et al. 2002). Due to soil and landscape factors, most intensive agricultural activities in the Upper Susquehanna Basin are located near streams, and a large fraction is animal-based (mostly dairy). Moreover, the lands receiving N as manure and fertilizer are often coarse-textured valley-bottom soils that have high leaching potentials. This has created a situation where N may be readily discharged into the stream system through shallow groundwater. Most of the upper Susquehanna River basin is within a 10 minute to 1.5 hour drive of Cornell University, making it a convenient area of study for our faculty, staff, and students.
In 2004, the North American N Center was established at Cornell University as part of the International N Initiative (a joint effort of the International Council of Science’s IGBP and SCOPE programs). The goals of the Center are to better understand the sources and sinks of N across North America, to quantify the consequences of N pollution, and to provide scientific support for the development of technical and policy approaches for reducing N pollution (www.eeb.cornell.edu/biogeo/nanc/nanc.htm). The N Center has identified an improved understanding of N sources and sinks in Susquehanna River Basin as a priority area of study in North America, for the reasons presented above. This proposed research will directly support this priority.
Procedures and Approach to Research:

Our proposed research falls into two categories: 1) integrated modeling of nutrient and sediment sources and sinks across spatial scales; and 2) a series of creative, spin-up efforts emphasizing field or laboratory studies leading toward a better understanding of the sources and sinks of nutrients and sediments in the Susquehanna River Basin. For both of these, much of the research will be focused around two core sites within the basin that have long-term data records, one an agricultural site and one an atmospheric deposition site. These approaches to research and the research sites are described in detail below. The research addresses the dual needs for better understanding of the biophysical processes affecting N losses in the Basin, as well as the identification of management options for watershed abatement efforts. Although the processes controlling P fluxes are better understood, and P is less of a problem in Chesapeake Bay and most other coastal systems, much can be gained from studying N and P together (NRC 2000; Howarth & Marino, in press), and that is the approach we propose. These approaches to research and the research sites are described in detail below.

Integrated modeling across scales:

We will use 2 models at the scale of the entire upper Susquehanna River basin: the SCOPE/NANI model and the Regional Nutrient Management model (ReNuMa). We will explore how the insights and output from several smaller scale models can interact with these large watershed-scale models. The SCOPE/NANI model is a simple mass-balance model for N that compares sources of N in the landscape to riverine N fluxes. It was originally developed for large regions, such as the combined watersheds of the North Sea or the northeastern US, or the entire Mississippi River basin (Howarth et al. 1996), but has subsequently been applied to watersheds of the scale of the Susquehanna both in the U.S (Boyer et al. 2002) and in Europe (Humborg and colleagues, unpublished). Despite its simplicity, a comparative analysis of many models demonstrated that the SCOPE/NANI model is among the best in terms of error of prediction and assessment of N source determination (Alexander et al. 2002). The model when employed as we and most others have previously used it evaluates average N fluxes over periods of 6 to 10 years, but McIsaac et al. (2001) used a modification of the approach to accurately predict year-to-year variations in N flows in the Mississippi River that are associated with climatic variation. We will test this approach for the Susquehanna, in an effort to better determine the influence of climate on overall N fluxes, and to get insights into the relative importance of climate effect on different N source terms (Howarth et al., in press.).

The other model we will use at the large watershed scale is ReNuMa, a model designed to allow planners and other stakeholders to explore scenarios for reducing N fluxes from the landscape. We have been funded by the US EPA to develop ReNuMa, which is a refinement of the GWLF model of Haith and Shoemaker (1987). This lumped parameter model is an excellent predictor of freshwater discharge for the Hudson River and its tributaries on a fine temporal scale, and a good predictor of inputs of sediment and organic carbon on a monthly to seasonal time scale (Howarth et al. 1991; Swaney et al. 1996). GWLF has also been used to estimate nutrient loads into the Delaware River (Haith and Shoemaker 1987), the Tar-Pamlico estuary (Dodd and Tippett 1994), and the Choptank River drainage of Chesapeake Bay (Lee et al. 2000, 2001). However, the characterization of the N cycle within GWLF is excessively simple. For example, it does not include denitrification, which is the major sink for N in most watersheds (van Breemen et al. 2002). Rather, nutrients are transported passively, and within-soil, riparian-zone, and in-stream processes are not considered. GWLF also does not explicitly consider atmospheric inputs of N, even though these are the major nonpoint sources of N to many waters and watersheds in the northeastern US and elsewhere (Howarth et al. 1996, 2002b; NRC 2000; Boyer et al. 2002). Further, GWLF assumes specified values for nutrient concentrations from fertilizer or manure applications, irrespective of management practices and other mitigating factors. In developing ReNuMa, we are adding modules to better capture biogeochemical complexity and the relationship between hydrology and nutrient sources and sinks in the landscape, as well as for the effects of management practices on nutrient loads. We have limited funding from the USDA Hatch program ($15,000 per year) to begin to apply ReNuMa to the Susquehanna basin. This additional funding will enhance our ability to parameterize the model to the Susquehanna. We also propose to use output from the SCOPE/NANI model to improve the ability of ReNuMa to predict the consequences of climate variability and climate change on delivery of N. And we will use insights gained from plot- to farm-scale models to better parameterize the responses of ReNuMa to agricultural practices (see discussion below on these models). Both the SCOPE/NANI approach and ReNuMa will be ground-truthed against the accumulating body of data on fluxes of water, N, P, and sediments from the upper Susquehanna River basin being collected by the USGS, the NYS DEC, and others.
There are a large number of models that address fluxes of nutrients at the scale of plots to farm fields to whole farms, including several models developed and used by Cornell faculty and staff. These models often have a great deal more complexity and spatial reality than do the coarser scale large watershed models such as SCOPE/NANI and ReNuMa. On the other hand, their complexity and detail tend to make them difficult to scale up to give reliable estimates on watershed-scale nutrient fluxes (NRC 2000). Using insights gained from one scale of modeling to inform modeling at a different spatial scale, although challenging, is highly desirable. We propose to facilitate such an interaction of modeling efforts across scales in the Susquehanna River basin. One goal is to improve the utility of the integrative watershed model ReNuMa, as stated above. Beyond this, we believe the cross-fertilization of ideas may lead to improved models at smaller scales as well, and to an improved understanding of the processes that are critical in determining the fluxes and sinks of N and P (and where in the landscape such processes may be most important to understand). One approach to crossing this scale divide includes statistical comparisons of model outputs when models are subject to similar input perturbations, such as extreme weather events. Another approach is to use the model research at smaller scales to better identify and describe the critical processes that may control the overall behavior of large watersheds. For example, preferential flowpaths may be characterized by their relationship to soil types. Various categories of land and crop management may be summarized in terms of their effects on hydrology, soil loss, or chemical processes. This level of information can be considered a “typology” or classification system derived from detailed process studies, and can in turn be used as a basis for simplified models or “decision support tools” at larger scales. An approach like this has been taken in Sweden to develop the SOILNDB system, based on the models SOIL and SOILN (http://www.mv.slu.se/vv/model/e_soilndb.htm).
Given the large number of smaller scale models of potential value to the overall goals of the project, we propose to have a competitive process for selecting both for the model studies that may offer the best opportunity to scale up insights, and for researchers who are most open to undertaking this challenging endeavor. The expectation is that support will be available for 2 to 3 modeling efforts, developed over a multi-year time period. The required emphasis for supported research will be on integration across scales, and understanding the flows of nutrients and sediment in the Susquehanna, and not on the development of new models per se. Thus, the expectation is that only small spatial scale modeling efforts that already have other sources of support will be further funded by this Susquehanna project. An example of one such model is the recently-developed PNM (Precision N Management) model that allows for simulation of soil N dynamics and crop uptake and can be applied to better estimate seasonal crop N needs as well as predict N leaching from the soil profile. This model can also be used to estimate N losses from organic and inorganic sources on agricultural fields in the basin and to evaluate potential reductions in environmental losses from alternative management practices. Another example model might be a statistical meta-data analysis that relates nitrate concentrations below rooting zones to agricultural practices across a broad range of soils types and climate. And a third example model might be the Soil Moisture Routing Model (SMR) developed at Cornell for small watersheds where soil saturation is largely controlled by interflow (Zollweg et al. 1996; Frankenberger et al. 1999). This hydrologic model works with a grid size of 10 m X 10 m and has recently been applied to estimating the loss of P from manures applied to fields (Gérard-Marchant et al. 2005). Again, these models are given here just as examples, and we anticipate that other modeling projects will be proposed by Cornell faculty, staff, and students as part of this competition. We will use peer-review and a selection committee to choose those deemed most likely to fulfill the overall Agricultural Ecosystem Program goals. We will also develop processes to ensure interaction and integration among these modeling projects (such as regular meetings).
Creative spin-up research efforts:

The Cornell community has extensive depth of expertise that can support the central research objectives, and we propose to tap into this in a manner to maximize the development of new, creative science. Towards this end, the project will support a series of meso-size start-up grants for new research efforts directly related to the overall project objectives and a series of mini-grants to augment current research and encourage its application to the understanding of the Susquehanna River basin. These awards will be made on a competitive basis to faculty, staff, and students in the College of Agriculture and Life Sciences and related departments. We envision supporting four of the meso-size grants, averaging $30,000 each year over two years (contingent on future funding). The expectation is that some of these will lead to larger, more sustained research in the Susquehanna Basin, using other sources of support. The research can be at a variety of spatial scales (micro, plot-scale, farm or small watershed scale, or large watershed), and can be either lab- or field-based, but it must be directly applicable to understanding nutrient fluxes in the landscape of the Susquehanna and opportunities to reduce downstream losses. Examples of such research might be using genomic markers to locate hot spots of denitrifier activity, evaluating the N status of forests in the basin and their tendency to store versus export depositional N inputs, determining the rates of N fixation by agricultural crops in the basin and the fate of that fixed N, evaluating the role of soil health in nutrient retention and losses, evaluating the volatilization of ammonia from manure on dairy farms in the basin, determining the potential for reducing farm-scale N and P pollution through changes in diet fed to milk cows, investigating soil and crop management techniques to reduce N and P input as well as leaching/runoff, for example through tillage, organic soil management or cover crops, and studying the relationship between water residence time and loss of N through denitrification in riparian wetlands and first-order streams. These are given as examples only, and we have no predisposed tendency to support a particular research topic. The criteria for funding will be the creativity of the idea, the potential to shed new insights on fluxes of nutrients and sediments in the Susquehanna River Basin, the opportunities to reduce these environmental risks, and the likelihood that the project will lead to a longer term sustained research effort. High risk projects (those unlikely to receive initial funding from traditional funding sources, yet may have potentially large pay-offs) will be encouraged. To maximize the ability for interested researchers to see opportunities for coordination and collaboration on proposal, preproposals may be used to screen topics and to develop a list of proposed projects to circulate among the Cornell community.

For the mini-grants, we envision perhaps 10 awards of $1,000 to $3,000 each. These will be modeled after successful programs previously run at Cornell, such as the mini-grants of the NSF-funded Research Training Grant in Biogeochemistry & Environmental Change or the Cornell Center for the Environment. These are primarily aimed at graduate students. For a very modest investment, we can provide substantial help to thesis research while also directing some of the focus of student research towards the overall objectives of this proposal: understanding the sources and sinks of nutrients and sediments in the Susquehanna River Basin. By engaging the students, we believe we can also increase the awareness and engagement of the Cornell faculty in this area.
Both types of grants will be awarded on a competitive basis by a committee appointed by the PIs of this project, and each will receive peer review. The timing of calls for both types of proposals will be coordinated to achieve both the best diversity of pertinent research and the best overall integration of supported projects toward the program objectives. We will encourage interaction and foster collaboration among the funded efforts, using mechanisms such as web-based communications, list-serves, and workshops/seminars. To develop initial interest, we intend to hold a workshop that highlights the objectives of the overall project and the background context for nutrient pollution in general and for Chesapeake Bay and the Susquehanna basin in particular. Our web site will be designed to be used for data sharing and linking to other projects and information relating to nutrients and sediments in the Susquehanna River basin.
Long-term research sites:

We propose to encourage field-based research at two long-term research sites, whenever that is appropriate. This can help provide interaction among the component research efforts, and also provides sites with detailed and current databases for calibrating and testing our modeling efforts. The grant will augment support for these sites and compile previous data from the sites that is pertinent to the overall project objectives. One of the sites is a dairy farm operated by Cornell as a research and teaching center, and the other is an atmospheric deposition monitoring station in a state forest.

Harford Teaching and Research Center:

One of the sites is Cornell’s agricultural Teaching and Research Center in Harford, NY located in a valley varying from 1 to 3 km wide. This dairy and beef farm, owned and operated by Cornell, is typical of those located in the upper Susquehanna River basin. It includes approximately 526 hectares of cropland which has been in maize and alfalfa since 1979About 390 ha are used for the dairy operation exclusively. Like many farms in the region, the valley bottom land is intensively farmed while the steep hillsides are forested or are in permanent grassland. The university moved into the facility in 1973, and there are records from that time. There is a drainage divide is in the middle of the farm, with some water going to the St. Lawrence and some to the Susquehanna. Most of the intensively farmed land is in the Susquehanna. Most of the water drainage is ground water in deep gravel outwash aquifers. About 40% of the ground water is from the intensively farmed valley floor and the remainder from the surrounding hills. There are no farming operations above the farm (the land is owned by Cornell and is woodland).

A now-retired faculty member, David Bouldin, had 15-18 wells dug on the fields at the Harford Teaching and Research center and monitored water quality for ~ 15-20 years before his retirement in 2000. Karl Czymmek, an Extension Associate who is part of the Pro Dairy program at Cornell, has continued to take samples since Bouldin's retirement. Detailed nitrate data from the wells through the year exist for at least 1979-1981 and 1992-1994, in addition to more sporadic sampling over time. There was a 2-fold increase in nitrate from the well water between 1981 and 1994 with some variation among wells. One well in the middle of the most intensively farmed area exceeded the permissible level of nitrate-N (10 mg/kg). We have detailed data since the 1970s on soil test results (pH, P, potassium, and N availability) and crop yields. The farm currently has a CAFO plan, so that there are good records of manure and fertilizer applications that go back about 20 years. We also have data on the amount of nutrients brought onto the farm in the form of animal feed. The benefits of this site are clear: we have good knowledge of cow numbers, field management, soil test results and well water measurements dating back 20 years on a farm with soils and management characteristic of many in the region.
We propose to again intensively sample these wells (some of which need repair) over an annual cycle (monthly sampling), and we will measure dissolved organic N and ammonia in addition to nitrate. We will also begin to collect surface water samples for analysis of nutrients and sediments from drainage creeks and streams at the site. Sampling will be at least monthly, with an effort to also sample during storm events. We will analyze for sediments, nitrate + nitrite, ammonium, total dissolved N, soluble reactive P, total dissolved P, and particulate N and P, using the standard procedures of the Cornell Nutrient Analysis Laboratory (CNAL) in the Departments of Crop & Soil Sciences and Horticulture and the Biogeochemistry Analytical Facility in the Department of Ecology & Evolutionary Biology. We also will begin to monitor the deposition of ammonia and ammonium along gradients away from the farm site, using both bulk deposition measurements (Fahey et al. 1999) and passive samplers for ammonia gas in the atmosphere, as described in the next section.
Connecticut Hill Atmospheric Atmospheric and Precipitation Chemistry Research Site:

This site is located on a 6-hectare site within the Connecticut Hill State Forest. The site has been in continuous operation since 1976, and is part of the National Atmospheric Deposition Network (NADP site NY67), which measures wet deposition and monitors trends in precipitation chemistry. Complementing this work, in 1987 the site became one of the original locations to measure regionally representative dry deposition in the US, and is part if the Clean Air Status and Trends Network (CASTNet site CTH 110). The site was originally set up to study and monitor precipitation chemistry and deposition in an area selected to be regionally representative of a large geographical area uninfluenced by any local pollution sources such as power plants, urban centers, farms, or highways. The site is in an area of the Susquehanna River watershed surrounded by extensive forestlands (i.e. the 4500 ha NYS Connecticut Hill Game Management Area) as well as old field and pasture. Both the landscape (hill and valley) and land use are typical of other headwater sections of the Susquehanna River watershed in New York State. Thus, this site is an ideal location to monitor and advance the understanding of the atmospheric inputs of N and other atmospheric species influencing the Susquehanna River in New York State. The site is managed by the Institute of Ecosystem Studies (IES), under the direction of Gene Likens, director of the IES and adjuct professor at Cornell. The site is run by Tom Butler, working out of the Howarth lab at Cornell.

In addition to the NADP and CASTNet monitoring, other research at the site has included studies of throughfall versus inferentially measured dry deposition of N and sulfur species, the initial testing and use of passive samplers as measures of dry deposition of N species, including some not measured by CASTNet (NH₃ and NO₂), isotopic studies (¹⁵N, ¹⁸O and ¹⁷O) of wet and dry deposition to understand the sources of NO₃ deposition (ie vehicle vs non-vehicle NOx emissions), and the impact of changing emissions of SO₂ and NOx on wet and dry deposition of N, sulfur and acidity. This makes it one of the best studied sites in the country for atmospheric deposition. Nonetheless, as with other depositional monitoring sites, some significant uncertainties remain. One of these is the extent of dry deposition of N, particularly for gaseous N. At least 1/3 of the measured total N deposition at the sites is in the form of dry deposition, but not all components have yet been measured. We now propose further investigation of the use of passive samplers as measures of dry deposition for several N species including NH₃, NO₂, NO and HNO₃ (modified samplers). Some preliminary work is being done on the spatial and temporal variability of passive samplers (E. Boyer and C. Kendall, unpublished).
We will expand on this work to assess the comparability of passive sampler data (concentration estimates for various N species) with the filter pack measurements employed by the CASTNet measurements at this site. We will also test the spatial variability of dry deposition products, since elevation, slope aspect and proximity to roadways or other pollution sources can all impact rates of dry deposition of N, Further, we propose the real-time measurement of gaseous NH₃, and HNO₃ and NOy (as well as other atmospheric trace gases) using newly developed instrumentation that will be deployed at selected CASTNet sites, including this one. Measurement of these species using some of the latest instrumentation technologies will allow for the best estimates of the true atmospheric N deposition that is impacting the Susquehanna watershed. Calibrating the passive samplers to the results from these more detailed measurements will increase the usefulness of passive samplers as an approach that we and others can then use more broadly across the landscape for better estimation of spatial patterns of N deposition. Coupled with wet deposition measurements, these approaches will give us the best estimates of total N atmospheric deposition and the speciation of N. The quantification of currently unmeasured species ( NH₃ and NO₂) and more accurate measurements of other N species (HNO₃) will result in a better understanding of the relative importance of atmospheric N deposition.
Current Work:

Current related work includes the limited effort by the Howarth lab to apply the ReNuMa model to the upper Susquehanna River Basin (funded with USDA Hatch funds; $15,000 per year), as well work in the Howarth lab to further develop the structure for ReNuMa and apply it as well as the SCOPE/NANI approach across a variety of watersheds in North America and Europe (funded through the EPA STAR program). Other related research includes a new effort by Christy Goodale to begin to examine the status of N saturation in the forests of the upper Susquehanna River Basin (a one year starter grant from the USGS/Water Resources Institute for New York). Basic core support for the Connecticut Hill deposition monitoring station continues to be provided by EPA and by NOAA, and basic support for the Harford agricultural Research and Teaching Center is provided by Cornell. Further, there is a great deal of work by Cornell faculty, staff, and students on N and P dynamics at a variety of scales, from molecular to watershed.

Facilities and Equipment:

Field research facilities in addition to two core research sites described above include numerous research farms and experimental areas in close proximity to the Cornell campus. Controlled environment growth chambers and greenhouse space are widely available across campus. Cornell faculty research laboratory facilities are well-equipped with such items as UV, visible, and IR spectrophotometers, fluorometers, gas and liquid chromatographs, as well as field sampling equipment needed for agricultural and environmental research. Analytical facilities for nutrient analysis of soils, waters, and biological materials by simultaneous, multi-element ICP, continuous flow autoanalyzer, and C and N analyzer are available through the Department of Crop and Soil Sciences and the Department of Ecology and Evolutionary Biology. The mass spectrometer facility also in the Department of Ecology and Evolutionary Biology houses instruments with dual inlet and continuous flow capabilities, coupled to a Carlo Erba CNS analyzer for solid samples, and a Europa Geo 20-20 IRMS configured for continuous flow measurements on bulk samples and trace N₂and CO₂ measurements. This facility houses equipment for sample preparation needs, including freeze dryers, grinders, drying ovens, muffle furnaces, balances, and extraction prep lines. NSF-supported facilities include an NMR center in the chemistry department and a supercomputer center with an IBM 3090-600E mainframe with vector facilities and floating point system scientific computers. Cornell has an excellent library system, including one of the best agricultural libraries in the nation. Several micro-computing centers exist across campus; one is established primarily for GIS work. In addition the Northeast Regional Climate Center is housed at Cornell with historical and real-time climate data stores and information to assess the current climate conditions and its impact on regional economic sectors.

Project Timetable:

The watershed-scale modeling and the expanded work at the Harford and Connecticut Hill sites, described above, will begin with the start of the grant on August 15, 2005, and will continue through the year. We will set up committees and solicit proposals for the plot- to file- to farm-scale modeling as soon as we receive word that the proposal is funded, and make those awards as soon as practicable to ensure optimum interaction with the watershed-scale modeling over the year. We will set up a web site for the project in August, and announce the project to the Cornell community through a variety of on-campus list serves at that time. We intend to hold the workshop for the project in September. We will ask for pre-proposals for meso-scale grants in October, and solicit full proposals (with our feedback) for the meso-size grants that will be due in November. Mini-grants will also be due at that time. We will make awards in December, and encourage full interaction among these components for the rest of the grant year.

Key Personnel:

The project is under the overall control of a faculty committee appointed by the College of Agriculture and Life Sciences at Cornell, and reports to Bill Fry, Senior Associate Dean for the College. The committee consists of Nelson Hairston (Department of Ecology & Evolutionary Biology), Bob Howarth (Department of Ecology & Evolutionary Biology), Johannes Lehmann (Department of Crop and Soil Sciences), and Alice Pell (Department of Animal Sciences). The committee developed the focus for this proposal, with principal investigators Howarth, Lehmann, Pell, and Roxanne Marino (Department of Ecology & Evolutionary Biology). The committee and PIs will work jointly to fulfill the goals of the project, and will have responsibility to appoint committees for the development of further modeling activities across scales, for the award of meso-size grants, and for award of mini-grants. Howarth will chair the overall effort and serve as project director for the grant. He will also supervise the coordination of the modeling efforts. Pell and Lehmann jointly will be responsible for the work at the Harford agricultural Teaching and Research Center. Marino will be responsible for oversight of the work at the Connecticut Hill depositional monitoring site.

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