Living on the edge: The need for long-term management strategies to lessen the impact of climatic and anthropogenic changes on naturally stressed low inflow estuaries

Michael Wetz, Harte Research Institute for Gulf of Mexico Studies, Texas A&M University - Corpus Christi, Corpus Christi, TX

Background/Question/Methods
Low inflow estuaries are numerically significant on a global scale and are typical of seasonal or chronic low rainfall climates. Yet they are underrepresented in the literature compared to river-dominated estuaries. Thus, less is known about how they function, key stressors on their ecosystem health, and consequently on appropriate management strategies. Prolonged low inflows, salinity extremes, and long residence times suggest that these ecosystems are naturally stressed but are likely also susceptible to additional climatic and anthropogenic stressors. Using data collected as part of long-term monitoring programs in a low inflow Texas estuary (Baffin Bay-Upper Laguna Madre; BB-ULM), as well as a synthesis of findings from similar estuaries globally, this presentation will attempt to answer the following questions: • What are the current and projected future stressors upon low inflow estuaries?
• What are the singular or interactive effects of those stressors, and how do we manage for their effects?

Results/Conclusions
An emerging theme from this analysis is that low inflow estuaries are particularly susceptible to pollutant accumulation and eutrophication. For example, BB-ULM is displaying multiple symptoms of eutrophication, namely very high organic nutrient concentrations, high and increasing chlorophyll concentrations, fish kills, episodic hypoxia and a long-term decrease in dissolved oxygen levels. In addition, it has experienced recurring, multiyear blooms of the harmful alga Aureoumbra lagunensis (“brown tide”) since 1989. The eutrophication of BB-ULM is occurring despite it only receiving freshwater input (and associated nutrient loads) via episodic floods and flow from ephemeral streams. Efforts to alleviate these symptoms of eutrophication are complicated by the multitude of nutrient load sources as well as the presence of “legacy” nutrients in estuarine sediments. Furthermore, the symptoms have likely been exacerbated by a long-term seasonal increase in water temperature, effects of which include increased rates of nutrient cycling, increased algal growth rates, and lower dissolved oxygen levels. Moving forward in time, resource managers will need to contend not only with growing nutrient pressures facing many low inflow estuaries, but also the growing prevalence of interactive effects from increased water temperatures and decreased inflows/increasing residence times (due to climate change and increase human freshwater withdrawals).