Environmental Flow Requirements of Estuaries: Providing Resilience to Current and Future Climate and Direct Anthropogenic Changes

Abstract

Estuaries host unique biodiversity and deliver a range of ecosystem services at the interface between catchment and the ocean. They are also among the most degraded ecosystems on Earth. Freshwater flow regimes drive ecological processes contributing to their biodiversity and economic value, but have been modified extensively in many systems by upstream water use. Knowledge of freshwater flow requirements for estuaries (environmental flows or E-flows) lags behind that of rivers and their floodplains. Generalising estuarine E-flows is further complicated by responses that appear to be specific to each system. Here we critically review the E-flow requirements of estuaries to 1) identify the key ecosystem processes (hydrodynamics, salinity regulation, sediment dynamics, nutrient cycling and trophic transfer, and connectivity) modulated by freshwater flow regimes, 2) identify key drivers (rainfall, runoff, temperature, sea level rise and direct anthropogenic) that generate changes to the magnitude, quality and timing of flows, and 3) propose mitigation strategies (e.g., modification of dam operations and habitat restoration) to buffer against the risks of altered freshwater flows and build resilience to direct and indirect anthropogenic disturbances. These strategies support re-establishment of the natural characteristics of freshwater flow regimes which are foundational to healthy estuarine ecosystems.

Resilient rivers and connected marine systems: a review of mutual sustainability opportunities

“…Identifying hydrologic connectivity and flood dynamics to reduce escapement of non-native species and poor water quality spillover, particularly for pond-based aquaculture (Boyd et al, 2020), may help maintain river and estuary ecosystem health while also supporting food security. (3) Developing long-term gauging systems and watermonitoring programmes in rivers provides a crucial data prerequisite to understanding key estuarine and coastal ecosystem processes (Chilton et al, 2021). These can include hydrodynamics, salinity, regulation, sediment dynamics, nutrient cycling and trophic transfer and connectivity.…”

“…A data-driven approach directed at decision makers may be an effective means to build technical capacity and enable restoration particularly for freshwater systems and their estuaries. Freshwater aquaculture has the potential to boost food production from inland waters that cannot enhance capture-based production (Cooke et al, 2016; Gephart et al, 2021). Identifying hydrologic connectivity and flood dynamics to reduce escapement of non-native species and poor water quality spillover, particularly for pond-based aquaculture (Boyd et al, 2020), may help maintain river and estuary ecosystem health while also supporting food security. Developing long-term gauging systems and water-monitoring programmes in rivers provides a crucial data prerequisite to understanding key estuarine and coastal ecosystem processes (Chilton et al, 2021). These can include hydrodynamics, salinity, regulation, sediment dynamics, nutrient cycling and trophic transfer and connectivity.…”

“…3. Developing long-term gauging systems and water monitoring programmes in rivers provides a crucial data prerequisite to understanding key estuarine and coastal ecosystem processes (Chilton et al, 2021).These can include hydrodynamics, salinity, regulation, sediment dynamics, nutrient cycling and trophic transfer, and management actions (e.g., riparian buffers) (Lind et al, 2019;Van Niekerk et al, 2019)..…”

Prevalence of microplastics, antibiotic resistant genes and microplastic associated biofilms in estuary - A review

“…Tributaries transport nutrients into estuaries and transform them into highly productive ecosystems [1,2]. Further, estuaries are vital resources for providing food and habitat for fish and shellfish, food for human consumption, areas for tourism and recreation, and a host of ecosystem services [3][4][5]. Currently, the estuarine ecosystem is highly polluted [2] by several point and nonpoint sources, including agricultural runoff, wildlife excrement, septic tanks, and sewage discharges [6,7].…”

Occurrence of Coliforms in Microplastic Associated Biofilm in Estuarine Ecosystem

“…Distribution of feacal coliforms has been reported in rivers [4,5], lagoons [6], estuaries [7,8]. Among the different ecosystems, estuaries are considered as important resources, as estuaries are providing food and habitat for fish and shellfish, food for human consumption, areas for tourism and recreation and host of ecosystem services [9][10][11]. Currently, estuaries are polluted with human and animal release which contains a large amount of pathogenic microorganisms [12,13], and plastics [14].…”