Physicochemical and urban land-use characteristics associated with resistance to precipitation in estuaries vary across scales

Estuaries are subject to frequent stressors, including elevated nutrient loading and extreme hydrologic events, which impact water quality and disrupt ecosystem stability and function. The capacity of an estuary to resist changes in function in response to precipitation events is an important descriptor of ecosystem response dynamics, especially when interpreted within the context of baseline system condition and ecological state. However, the factors related to estuarine responses to extreme precipitation remain poorly constrained. This knowledge gap complicates our ability to identify estuaries that are more likely to undergo major shifts in ecosystem services and predict the effects of urban and precipitation disturbances on estuarine water quality. We investigate which physicochemical and land-use characteristics are associated with ecological resistance to precipitation – defined as the magnitude of ecosystem change induced by an event – in five disparate estuaries distributed across the continental United States. Using long-term meteorological and water quality data from the National Estuarine Research Reserve System along with land use/land cover and population data, we examine relationships between the resistance index – a proxy for ecosystem stability calculated using dissolved oxygen – and physicochemical and urban land use characteristics on local-to-continental scales. Contrary to our initial hypothesis, we found that more urbanized estuaries tended to be more resistant to precipitation events in this dataset, possibly due to persistent disturbances to their baseline dissolved oxygen levels, and that water temperature, water column depth, turbidity, nitrogen, and chlorophyll a showed significant but variable associations with resistance at the continental scale. These continental-scale patterns were modulated by estuarine salinity and varied across individual estuaries, where additional relationships between resistance and salinity, phosphate concentrations, N : P, tree cover, and cropland emerged. Our findings suggest that the relationships between urbanization and estuarine stability are complex and context-dependent, and thus management strategies need to consider both broad generalizations and local conditions. Considering emerging stressors from new environmental scenarios and from urbanization, these results may help improve representation of the impacts of disturbances in large-scale models and inform management decisions regarding estuarine water quality.