Nonpoint-source nitrogen and phosphorus behavior and modeling in cold climate: a review

Abstract

Pollution from nonpoint-source (NPS) nitrogen (N) and phosphorus (P) are the main causes of eutrophication in lotic, lentic and coastal systems. The climate of cold regions might play an important role in disturbing environmental behavior of NPS N and P, influencing simulation of watershed scale hydrologic and nonpoint-source pollution models. The losses of NPS N and P increase in regions of cold climate. In cold seasons, accumulations of N and P are accelerated in soil with increasing fine root and aboveground biomass mortality, decreasing plant nutrient uptake, as well as freezing soil. N and P transformation is disturbed by soil frost and snow. Moreover, factors such as physical disruption of soil aggregates, pollutant accumulation in snowpack, and snow melting can all increase the NPS N and P losses to the waterbody. Therefore, NPS N and P in first flush are more serious in cold climate. All these effects, especially frozen soil and snowpack, make great challenges to watershed scale hydrologic and nonpoint-source pollution models simulation in cold climate. Model improvements of snowmelt runoff, nutrient losses in frozen soil, as well as N and P behavior have been initiated and will be continued to evaluate in terms of their performances and suitability with different scale, hydrologic and geologic conditions in the future.

Using an inverse modelling approach with equifinality control to investigate the dominant controls on snowmelt nutrient export

“…The methodology proposed is an attempt to address both the problems of equifinality in nutrient models (e.g., McIntyre et al, ; Zhang, Chen, & Yao, ) and the need for assessing the role of transport and fate of nutrients in cold regions (Costa et al, ; Han et al, ). Parameters were considered identifiable when any of the following two conditions were observed: (a) the difference between the NSE values obtained with the best simulation and the remaining simulations is higher than 5%, which suggests a unique parameter combination in the best simulation or (b) the variability of each parameter in the three best parameter combinations is smaller than 30% (Equation ), which suggests similar parameters in all three best parameter combinations: where NSE best is the NSE value of the best simulation, Parameter best are each of the parameters included in the best parameter combination, is the standard deviation of the NSE values of the three best simulations, and is the standard deviation of each of the parameters included in the three best parameter combinations.…”

“…Finally, rapidity of snowmelt and its importance to nutrient budgets may necessitate the use of high‐resolution temporal scales for modelling. Specifically, snowmelt occurs during a short period but has a major impact on the annual nutrient export (e.g., Costa et al, ; Han et al, ), suggesting that subdaily simulations may be necessary, and practices such as using cumulative monthly export as a test of model fit is likely to overlook important temporal dynamics. Several catchment‐scale models exist that allow for process‐based nutrient simulation in cold climates (e.g., HYdrological Predictions for the Environment, Arheimer, Dahné, Donnelly, Lindström, & Strömqvist, ; Hydrological Simulation Program‐Fortran, Duda, Hummel, Donigian, & Imhoff, ; Integrated Model of Nitrogen in Catchments, Arnold et al, ; and Soil and Water Assessment Tool, Borah & Bera ).…”

“…Several catchment‐scale models exist that allow for process‐based nutrient simulation in cold climates (e.g., HYdrological Predictions for the Environment, Arheimer, Dahné, Donnelly, Lindström, & Strömqvist, ; Hydrological Simulation Program‐Fortran, Duda, Hummel, Donigian, & Imhoff, ; Integrated Model of Nitrogen in Catchments, Arnold et al, ; and Soil and Water Assessment Tool, Borah & Bera ). Applications of these models have been primarily in regions where users believe that rainfall–run‐off is the primary transport process (Han et al, ), and so their performance in representing cold regions hydrology processes is normally not evaluated. However, there are clear deficiencies in the representation of key cold region hydrological processes that make their application in snowmelt‐dominated regions and frozen soils problematic.…”

“…The ability to predict nutrient export is important to support the development of effective land management practices, but it remains a major scientific challenge (Han, Xu, Liu, & Lian, 2010). Hydrochemistry and nutrient export from cold agricultural regions are affected by snow processes such as wind redistribution of snow, heterogeneous snowcover depletion, and rapid snowmelt and by agricultural practices such as fertilizer application, stubble management, tillage, and wetland drainage (Costa et al, 2017;Kling, Watson, McCullough, & Stainton, 2011).…”

“…Applications of these models have been primarily in regions where users believe that rainfall-run-off is the primary transport process (Han et al, 2010), and so their performance in representing cold regions hydrology processes is normally not evaluated. However, there are clear deficiencies in the representation of key cold region hydrological processes that make their application in snowmelt-dominated regions and frozen soils problematic.…”