Importance of landscape heterogeneity in sustaining hydrologic ecosystem services in an agricultural watershed

Abstract

The sustainability of hydrologic ecosystem services (freshwater benefits to people generated by terrestrial ecosystems) is challenged by human modification of landscapes. However, the role of landscape heterogeneity in sustaining hydrologic services at scales relevant to landscape management decisions is poorly understood. In particular, the relative importance of landscape composition (type and proportion of land cover) and configuration (spatial arrangement of cover types) is unclear. We analyzed indicators of production of three hydrologic services (freshwater supply, surface and ground water quality) in 100 subwatersheds in an urbanizing agricultural landscape (Yahara Watershed, Wisconsin, USA) and asked: (1) How do landscape composition and configuration affect supply of hydrologic services (i.e., does spatial pattern matter)? (2) Are there opportunities for small changes in landscape pattern to produce large gains in hydrologic services? Landscape composition and configuration both affected supply of hydrologic services, but composition was consistently more important than configuration for all three services. Together landscape composition and configuration explained more variation in indicators of surface‐water quality than in freshwater supply or groundwater quality (Nagelkerke/adjusted R2: 86%, 64%, and 39%, respectively). Surface‐water quality was negatively correlated with percent cropland and positively correlated with percent forest, grassland and wetland. In addition, surface‐water quality was greater in subwatersheds with higher wetland patch density, disaggregated forest patches and lower contagion. Surface‐water quality responded nonlinearly to percent cropland and wetland, with greater water quality where cropland covered below 60% and/or wetland above 6% of the subwatershed. Freshwater supply was negatively correlated with percent wetland and urban cover, and positively correlated with urban edge density. Groundwater quality was negatively correlated with percent cropland and grassland, and configuration variables were unimportant. Collectively, our study suggests that altering spatial arrangement of land cover will not be sufficient to enhance hydrologic services in an agricultural landscape. Rather, the relative abundance of land cover may need to change to improve hydrologic services. Targeting subwatersheds near the cropland or wetland thresholds may offer local opportunities to enhance surface‐water quality with minimal land‐cover change.

Role of wetlands in mitigating the trade‐off between crop production and water quality in agricultural landscapes

“…In contrast, Cheng and Basu (2017) have shown that given the same loss in wetland area, the nutrient removal potential lost is larger when smaller wetlands are lost from the landscape. In accord with the results of Qiu and Turner (2015), the relative abundance of wetland cover was more important in the study watershed (Appendix S1: Table S5). We also identified some characteristics of wetlands in the subwatersheds with relatively high mitigation effectiveness scores.…”

“…However, because nitrogen can be permanently removed from surface water via denitrification (Jordan et al 2003, Craig et al 2008, Roley et al 2012, much recent attention has focused on the question of whether watershed management may reduce downstream nitrate export without loss of agricultural function (Craig et al 2008). Some studies have suggested the possibility of ameliorating the trade-off between crop production and water quality by enhancing buffering capacity, including maintenance and restoration of wetlands, which remove nitrate effectively (Zedler 2003, Qiu and Turner 2015, Doody et al 2016, Hansen et al 2018.…”

Scenarios reveal pathways to sustain future ecosystem services in an agricultural landscape

“…This large spatial variability has several implications: (1) a particular service could either increase or decrease at a given location depending on future pathways, underscoring the power of local actions and fine‐scale management; (2) it is critical to identify areas most susceptible to future social‐ecological changes to maximize benefits of management using, for example, spatially explicit land‐use planning (Bateman et al. , Qiu and Turner ) or spatially targeted policy applications (Qiu et al. ); (3) most locales showed increases in some services but declines in others (rarely increases for all), indicating the persistence of spatial trade‐offs (Rodríguez et al.…”

“…Such heterogeneity likely resulted from prevailing spatial patterns in human drivers and geophysical properties, in conjunction with different assumptions of each scenario. This large spatial variability has several implications: (1) a particular service could either increase or decrease at a given location depending on future pathways, underscoring the power of local actions and fine-scale management; (2) it is critical to identify areas most susceptible to future social-ecological changes to maximize benefits of management using, for example, spatially explicit land-use planning (Bateman et al 2013, Qiu andTurner 2015) or spatially targeted policy applications (Qiu et al 2017); (3) most locales showed increases in some services but declines in others (rarely increases for all), indicating the persistence of spatial trade-offs (Rodr ıguez et al 2006, Qiu andTurner 2013) and need to account for these interactions in future landscape management; (4) watershed-level changes could mask geographic variations, which may be much greater in magnitude (e.g., soil carbon) or differ in direction from watershed changes. Understanding causes and mechanisms for changes in distinct locations or areas of disproportionate importance could shed light on how to manage lands for improving services at finescales, so as to lead to cumulative effects at the watershed scale.…”

Land Cover, Land Use, and Climate Change Impacts on Endemic Cichlid Habitats in Northern Tanzania

“…Fragstats 4.1 was used to calculate patch and class level statistics [74]. Evidence suggests that reporting solely the total area of natural vegetation in a catchment is insufficient and that the spatial configuration and quality of the patches of natural vegetation are also important considerations [30,[75][76][77]. At the patch level, we analyzed the distribution of the number of natural vegetation fragments for each period as a proxy for measuring landscape composition and configuration.…”