Joel Moore

Influence of Modern Stormwater Management Practices on Transport of Road Salt to Surface Waters

Application of road salts in regions with colder climates is leading to ground and surface water contamination. However, we know little about how modern stormwater management practices affect the movement of road salt through urban watersheds. We investigated groundwater contamination and transport of road salts at two stormwater ponds in Baltimore County, Maryland. In association with the ponds, we documented a plume of contaminated groundwater that resulted in Cl- loadings to the adjacent stream of 6574 to 40 008 kg Cl- per winter, depending on winter snowfall. We also monitored Na+ and Cl- ion concentrations and the temporal dynamics of conductivity at a range of stream sites in watersheds with and without stormwater management ponds. Streams draining watersheds with stormwater ponds had consistently higher conductivities and Cl- concentrations during base flow conditions and often exhibited greater peaks in Cl- and conductivity associated with winter storms and subsequent melting events, despite the degree of watershed development. Our results indicate that modern stormwater management practices are not protecting surface waters from road salt contamination and suggest they create contaminated plumes of groundwater that deliver Cl- and Na+ to streams throughout the year.

Steady-State Land Cover but Non-Steady-State Major Ion Chemistry in Urban Streams

Sources of many major ions in urban streams remain ambiguous, particularly for ions unrelated to deicing salt use, and temporal patterns in concentrations are unstudied. We used 16 years of water chemistry data based on weekly samples from the Baltimore, MD, USA, metropolitan area and the Weighted Regressions on Time, Discharge, and Season approach to investigate connections between major ions, land cover, and time. All watersheds were underlain by silicate bedrock, contained no regulated point sources, and had stable land cover. Major ion concentrations were higher with greater urban land cover. Notably, concentrations of most ions increased with time in (sub)urban streams and had higher annual variability than in watersheds without impervious surface cover. Nonpoint source contributions from deicing salt and concrete were the predominant influences on major ion concentrations and produced stream chemistry that was distinctly different from forested streams. The novel finding that concentrations of most major ions were not only elevated but increasing in urban streams even with no substantial changes in land cover during the study period has important implications for ecosystem health and water quality, particularly given recent work demonstrating the high correlation between elevated ion concentrations and changes in freshwater biotic communities.

Aquatic Ecosystem Impacts of Land Sharing Versus Sparing: Nutrient Loading to Southeast Asian Rivers

As world food demand continues to increase, two broad strategies for agricultural production have been widely discussed: land sparing and land sharing. Reflecting tradeoffs between the extent and intensity of agricultural use, land sparing maximizes the ratio of conserved to agricultural land, whereas land sharing allows more extensive, nature-friendly transformation of the agroecological matrix. Freshwater ecosystems are rarely considered in weighing these strategies, despite being strongly affected by land-use change. Here we analyze how shifting from extensive to intensive agricultural practices is altering dry season riverine nutrient availability and algal growth in upland Southeast Asia, which is experiencing rapid conversion from swidden—or shifting—cultivation to fertilized row crops. In situ algal growth assays and nutrient concentration data from eleven catchments representing a spectrum of land use and population densities show that intensive agriculture is associated with significantly elevated nitrate concentrations but no shift in phosphorus. As a result, nitrogen to phosphorus ratios increases dramatically, shifting algal growth toward colimitation by nitrogen and phosphorus. Geochemical analysis of suspended solids suggested comparable geological inputs across basins, but dissolved rare earth elements reveal that inorganic fertilizers are changing water chemistry in parallel with land use. Taken together, our analyses suggest that the transition from low-input land-sharing management (swidden) to high-input land-sparing practices (intensive row-crop agriculture) underway in Southeast Asia has profound consequences for river ecosystems. Such nutrient loading can affect river productivity and food webs, suggesting that land-use conservation strategies for Southeast Asia need to account for impacts on freshwater ecosystems.