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

Jiangxiao Qiu,Monica G Turner

doi:10.1890/es15-00312.1

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.

Highlights

Human domination of the biosphere is reshaping landscape heterogeneity that is critical for numerous ecological processes such as nutrient dynamics, energy flow and movement of organisms and materials (Turner et al 2001, Foley et al 2005, Kareiva et al 2007)
We averaged indicators of hydrologic services estimated at 30-m resolution for each subwatershed as response variables, and calculated selected landscape metrics using 30-m land use/cover data for each subwatershed as predictor variables, which were analyzed to examine relationships between landscape pattern and hydrologic services
Does spatial pattern matter? Our results suggested that landscape composition and configuration both mattered for supply of hydrologic services, but composition had by far the stronger influence (Fig. 4, Table 4)

Summary

Introduction

Human domination of the biosphere is reshaping landscape heterogeneity that is critical for numerous ecological processes such as nutrient dynamics, energy flow and movement of organisms and materials (Turner et al 2001, Foley et al 2005, Kareiva et al 2007). The links between landscape pattern and simultaneous provision of multiple ecosystem services, as well as the mechanisms underlying these relationships, are not well understood This presents a significant challenge for management practices that attempt to alter landscape pattern to sustain and enhance ecosystem services in a changing world. Hydrologic services are especially susceptible to landscape changes such as agricultural expansion or urbanization (Kepner et al 2012) These changes can affect water quantity or quality by altering ecohydrological processes and introducing contaminants (Brauman et al 2007, Kepner et al 2012). Expansion of urban impervious surface can increase ‘‘flashiness’’ of runoff from heavy rainfall events, resulting in more frequent and severe floods (Allan 2004) These landscape changes may interact with other drivers such as changing climate to challenge the sustainability of hydrologic services

Methods

Results

Discussion

Conclusion