Reassessing the relationship between landscape alteration and aquatic ecosystem degradation from a hydrologically sensitive area perspective

This study applies a novel landscape approach to empirically assess the linkage between terrestrial landscape alteration such as urbanization and aquatic ecosystem degradation from a hydrological sensitive area (HSA) perspective in 141 selected northern New Jersey watersheds. HSAs are hydrological “hotspots” in a watershed that actively contribute to runoff generation and were delineated using a soil topographic index. Land use metrics captured landscape alterations in terms of percentages of varying land uses in these watersheds and their HSAs. Aquatic ecosystem integrity was represented by a High Gradient Macroinvertebrate Index (HGMI) specifically developed for the stream types assessed in this study. Multiple linear regression (MLR) analysis was used to understand the relationships between land use metrics and HGMI score at the watershed- and HSA-scales and a data fitting procedure called Least Absolute Shrinkage and Selection Operator (LASSO) was used to identify the most statistically significant land use attributes to be retained in the MLR models. The modeling results at the HSA-scale showed more parsimonious and robust relationships between landscape alteration and aquatic integrity than at the watershed-scale in terms of both variable selection and statistical inference. While high intensity urbanization is a known stressor that can significantly degrade aquatic ecosystem integrity, the results indicate that landscapes developed more strategically by way of low intensity urbanization (e.g., rural residential) or on less hydrologically sensitive areas may lessen the detrimental effects of urbanization on aquatic ecosystem integrity. These findings support the premise that it is not just the extent of urbanization in a watershed that matters, but also the intensity and location of the disturbance on the landscape that affects aquatic ecosystem integrity. Such findings may encourage more flexible landscape planning and management practices that better protect HSAs from urban development in support of long-term aquatic ecosystem protection and restoration.