Kevin Dahms

Kevin Dahms

The results from this study can inform management decisions with regards to small urban estuaries that face immediate challenges associated with ecological degradation and long-term risks related to sea level rise.

2017 Urban Fellow

Research Topic: Water Quality and Hydrology

Faculty Advisor: Gaboury Benoit

Short-term Sediment Dynamics of Urban Estuaries under Altered Tidal Conditions

Estuaries along the Connecticut coast are important ecosystems that provide wildlife habitat and water quality improvement and flood mitigation services (1–3). Many of these estuaries are drowned stream valleys that were formed when the glaciers receded after the last ice age (3). Given the high rate of development along the coast, estuaries are often situated in urban areas (3,4), a condition which is certainly the case along the Connecticut coast of Long Island Sound (Figure 1). Urbanization around estuaries has resulted in the degradation of estuaries as they receive discharge from sewage treatment plants, contaminants in urban runoff, and elevated sediment supply associated with land use changes (3–7). The challenges facing estuaries are amplified by the effects of global climate change as sea levels rise, which is likely to significantly alter estuarine processes (2,8,9).
Understanding how development and sea level rise induced changes will impact these processes is essential to maintaining the health of these valuable ecosystems and the services they provide. Sediment dynamics represents one of the key processes controlling the functioning and health of estuaries. Sediment supply, deposition, and transport influence the health of benthic communities and marsh survival, which are key ecological components of estuarine systems (1,7,10). In addition, sediment is also heavily associated with the chemical and physical processes that drive contamination and water quality issues is estuaries (3,7,11). A study that improves the scientific community’s understanding of sediment dynamics will prove useful to managers aiming to restore or maintain estuaries along coastal regions.
Unfortunately, estuaries represent one of the most complex systems to in which to study sediment dynamics as they are influenced by both tidal fluxes and contributions from the watershed, which can vary on time scales from hours to days to weeks and even months or years (3,12). Additionally, the study of Connecticut’s urbanized drowned stream valley estuaries is relatively limited (3). A previous study by Benoit and coworkers (2016) developed a robust budget for one such estuary on the Branford River, however, the contribution of tidal flushing was inferred by difference (3). This represents a gap in knowledge of sediment dynamics since tidal mixing is a primary factor controlling circulation in northeastern estuaries (13). Therefore, this study aims to fill this gap by directly measuring and quantifying the influence of the tidal flushing term and watershed contribution in the sediment budget for a small drowned stream valley estuary at time scales ranging from individual daily tidal events, to monthly, along with individual storm events.