Quantifying Landscape Nutrient Inputs With Spatially Explicit Nutrient Source Estimate Maps

Abstract

Nutrient management is an essential part of watershed planning worldwide to protect water resources from both widespread landscape inputs of nutrients (N and P) and point source emissions. To provide information to regional watershed planners and better understand nutrient sources, we developed the Spatially Explicit Nutrient Source Estimate Map (SENSEmap) to quantify individual sources of N and P at their entry points in the landscape. We modeled seven sources of N and six sources of P across the U.S. Great Lakes Basin at 30‐m resolution: atmospheric deposition, septic systems, chemical nonagricultural fertilizer, chemical agricultural fertilizer, manure, nitrogen fixation, and point sources. By modeling these sources, we provide a more detailed view of nutrient inputs to the landscape beyond what would be possible from land use alone. We found that 71% and 88% of N and P, respectively, came from agricultural sources. The nature of agricultural nutrient inputs varied significantly across the basin, as relative contributions of chemical agricultural fertilizers, manure, and N fixation changed according to diverse land use practices regionally. We then applied k‐means cluster analysis and identified nine Nutrient Input Landscapes (NILs) with N and P source characteristics, grouped into intensive agricultural, urban, and rural landscapes. These NILs can offer insights into landscape variability that land use data alone cannot; within agricultural NILs, application of chemical fertilizer and manure varied greatly, but land uses were similar. These NILs can provide a framework for broadly categorizing watersheds that may prove useful to both ecological and management practices.

Long‐Term Shifts in U.S. Nitrogen Sources and Sinks Revealed by the New TREND‐Nitrogen Data Set (1930–2017)

“…To provide finer spatial resolution, Swaney et al (2018) have developed a county‐scale data set of anthropogenic N inputs and outputs covering much of the contiguous United States, and Sabo et al (2019) have built upon this work to provide more complete geographic coverage and a more inclusive inventory of N inputs. In addition, Hamlin et al (2020) have developed estimates of landscape N inputs across the Great Lakes region at a 30‐m spatial resolution. All of these data sets, however, are limited in their temporal extent.…”

Hydrologic flushing rates drive nitrogen cycling and plant invasion in a freshwater coastal wetland model

“…We simulated the relevant conditions reported at each sentinel site in Mondrian, including annual average temperature, temperature range, growing season length, water level, N inputs, and plant community (Table 1). For sites that did not report both and inputs, we used a 1:3 ratio of ‐N: ‐N, typical of land use dominated by high‐intensity agriculture in which these sites were situated (Hamlin et al 2020). We then adjusted both θ n and θ d to achieve a best fit using a residual sum of squares (Fig.…”

“…In addition to hydroperiod and RT h , we used six levels of N loading, ranging from oligotrophic, precipitation‐fed wetlands (1 g N·m −2 ·yr −1 ) to highly eutrophic wetlands (100 g N·m −2 ·yr −1 ; Krieger 2003). We then partitioned the six levels of N loading into ‐N and ‐N proportions that included conceptual ‐only or ‐only N inputs as end points, together with three ‐N : ‐N ratios that characterize wetland N loading from three dominant land use classes in the region: urban (1:7.3), high‐intensity agriculture (1:3), and rural (4:1; Hamlin et al 2020). Finally, we simulated plant communities in which either Phragmites australis or Typha × glauca , two common invasive species in the Great Lakes region, are introduced into established communities comprising three native wetland species: Eleocharis smallii , Juncus balticus , and Schoenoplectus acutus .…”

“…We examine various hydroperiod frequencies with the same flooding range and total number of flooded days but with different flooding duration, in addition to wetlands with constant low and high water level. We also examined N loading with various nitrate () to ammonium () ratios as N removal and transformation processes can require one or the other species and because these ratios vary across the landscape (Hamlin et al 2020; L. Wan, personal communication ). We then assessed how these conditions influence N removal in two ways: annual N removal (i.e., the total N mass removed from an area in a given time) and N removal efficiency (i.e., N removed and denitrified relative to N entering wetlands).…”

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

“…Regional water quality models of the Mississippi River basin estimated that croplands, pasturelands, and rangelands delivered about 80% of P loads to the Gulf of Mexico from 1992(Alexander et al, 2008, and a global study of grey water footprints estimated that agricultural land accounted for 38% of anthropogenic P loads to freshwater from 2002 to 2010 (Mekonnen & Hoekstra, 2018). A recent watershed modeling study estimated that 88% of P inputs into the Great Lakes Basin came from agricultural sources (Hamlin et al, 2020), which have contributed to regional eutrophication issues for more than 50 years (Chapra and Dolan, 2012;Dolan and Chapra, 2012). In addition to various model estimates, long-term monitoring records emphasize the impact of agriculture on P pollution.…”