Sandbar Breaches Control of the Biogeochemistry of a Micro-Estuary

Abstract

Micro-estuaries in semi-arid areas, despite their small size (shallow depth of a few meters, length of a few kilometers, and a surface area of less than 1 km 2 ) are important providers of ecosystem services. Despite their high abundance, tendency to suffer from eutrophication and vulnerability to other anthropogenic impacts, such systems are among the least studied water bodies in the world. In low tidal amplitude regions, micro-estuaries often have limited rate of sea-river water exchange, somewhat similar to fjord circulation, caused by a shallow sandbar forming at the coastline. The longterm study, we report here was inspired by the idea that, due to their small size and low discharges regime, relatively small interventions can have large effects on micro-estuaries. We used a stationary array of sensors and detailed monthly water sampling to characterize the Alexander estuary, a typical micro-estuary in the S.E. Mediterranean, and to identify the main stress factors in this aquatic ecosystem. The Alexander micro-estuary is stratified throughout the year with median bottom salinity of 18 PSU. Prolonged periods of hypoxia were identified as the main stress factor. Those were alleviated by breaching of the sandbar at the estuary mouth by sea-waves or stormwater runoff events (mostly during winter) that flush the anoxic bottom water. Analysis of naturally occurring sandbar breaches, and an artificial breach experiment indicate that the current oxygen consumption rate of the Alexander micro-estuary is too high to consider sandbar breaches as a remedy for the anoxia. Nevertheless, it demonstrates and provides the tools to assess the feasibility of small-scale interventions to control micro-estuaries hydrology and biogeochemistry.

Metazoan activity facilitates passive sediment trapping in modern supratidal microbialites: Revealed using µ‐CT‐scanning and microscopy

“…Bernhard et al, 2013;Riding, 2011b), although abiotic environmental influences, such as hydrodynamics, hydrochemistry and sediment availability, may also have a significant influence (e.g. Golubic, 1973;Suarez-Gonzalez et al, 2019;Suari et al, 2019;Vennin et al, 2015). ing both layered and non-layered varieties.…”

Multi-Scale Modeling of Intensive Macroalgae Cultivation and Marine Nitrogen Sequestration

“…in a row of cultivation reactors in a nutrient-enriched estuary environment located in a semi-arid climate. Data regarding nutrient concentrations, salinities, water temperature and flow was taken from the long-term study of Suari et al 59 on the Alexander estuary, located in the center of Israel (SI appendix, Fig. S12 and Table S4).…”

“…I data was extracted from the IMS database from the Israel Meteorological Services (https://ims.data.gov.il/he/ims/6). Although S varies with depth and can change dramatically according to flesh flood events and formation of sandbar breaches 59 , effect on growth was minor and we used a constant value of S=30 PSU. All constraining environmental factors except nutrients were assumed to be constant in space.…”

Ten Principles to Determine Environmental Flow Requirements for Temporarily Closed Estuaries

“…An estuarine health index is applied to measure the present state from a reference condition taken approximately 120 years ago, before large-scale urban and water resource development occurred in South Africa. The index rates estuaries from 0 to 100 as natural (91-100), largely natural (74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90), moderately modified , largely modified , and highly degraded to extremely degraded (20-0) [42,43]. Changes in health state provide a measure of how resilient an estuary is to changes in EFlows.…”

“…Reduced water residence times and elevated salinity limited the occurrence of harmful algal blooms, bacterial contamination, and fish kills [87]. However, artificial breaching as a flow mitigation measure without supporting freshwater input from the catchment can result in reduced water column depth and increases stress on resident biota by exposing communities to low oxygen bottom waters that occur in enriched systems [88][89][90]. Artificial breaching is thus not advocated as a mitigation for poor water quality and this should rather be addressed at source.…”