Effects of land use on benthos and nekton communities in adjacent estuaries over 30 years

Estuaries are ecologically and economically important ecosystems, yet their health is increasingly at risk due to anthropogenic pressures of growing human populations. Land uses and land covers (LULC) are constantly changing within watersheds, which can affect downstream estuaries as freshwater inflows transport pollutants, nutrients, and sediments to receiving waters. The relationship between land-use changes and their effect on estuarine response in five Texas coastal watersheds (Lavaca-Colorado, Guadalupe, Mission-Aransas, Nueces, Laguna Madre) were investigated over a 30-year span. Changes in LULC were quantified and then correlated with water quality, diversity, and abundance of benthic and adult and juvenile nekton species. Two ecological gradients were discovered using principal components analysis (PCA): a nutrient loading and freshwater inflow gradient (PC1) that explained 37% of the variance and a biological abundance gradient (PC2) that explained 19% of the variance. There was a negative correlation between PC1 and developed lands, which could be due to decreased freshwater inflow leading to less nutrient delivery. There was a positive correlation between PC1 and forests and wetlands, which reflects their ecosystem services as nutrient sources. There was a strong negative correlation between PC2 and developed lands, demonstrating that altered hydrology in urbanized areas was related to a decrease in estuary organismal abundance. Total watershed land use diversity was positively correlated with PC1 indicating diverse landscapes may provide multiple ecosystem services that help regulate freshwater inflow and nutrient balance. This study demonstrates that the quantity, quality, and timing of freshwater inflow is shaped by upstream land use, and they are critical for sustaining estuary community abundance and diversity.