Seawater intrusion: an appraisal of taxa at most risk and safe salinity levels

Abstract

Seawater intrusion into low‐lying coastal ecosystems carries environmental risks. Salinity levels at these coastal ecosystems may vary substantially, causing ecological effects from mortality to several sublethal endpoints, such as depression of rates of feeding, somatic growth, or reproduction. This review attempts to establish safe salinity levels for both terrestrial and freshwater temperate ecosystems by integrating data available in the literature. We have four specific objectives: (i) to identify the most sensitive ecological taxa to seawater intrusion; (ii) to establish maximum acceptable concentrations–environmental quality standards (MAC‐EQSs) for sea water (SW) from species sensitivity distributions (SSDs); (iii) to compile from the literature examples of saline intrusion [to be used as predicted environmental concentrations (PECs)] and to compute risk quotients for the temperate zone; and (iv) to assess whether sodium chloride (NaCl) is an appropriate surrogate for SW in ecological risk assessments by comparing SSD‐derived values for NaCl and SW and by comparing these with field data. Zooplankton, early life stages of amphibians and freshwater mussels were the most sensitive ecological receptors for the freshwater compartment, while soil invertebrates were the most sensitive ecological receptors for the terrestrial compartment. Hazard concentration 5% (HC5) values, defined as the concentration (herein measured as conductivity) that affects (causes lethal or sublethal effects) 5% of the species in a distribution, computed for SW were over 22 and 40 times lower than the conductivity of natural SW (≈ 52 mS/cm) for the freshwater and soil compartment, respectively. This sensitivity of both compartments means that small increments in salinity levels or small SW intrusions might represent severe risks for low‐lying coastal ecosystems. Furthermore, the proximity between HC5 values for the soil and freshwater compartments suggests that salinized soils might represent an additional risk for nearby freshwater systems. This sensitivity was corroborated by the derivation of risk quotients using real saline intrusion examples (PECs) collected from the literature: risk was >1 in 34 out of 37 examples. By contrast, comparisons of HC5 values obtained from SSDs in field surveys or mesocosm studies suggest that natural communities are more resilient to salinization than expected. Finally, NaCl was found to be slightly more toxic than SW, at both lethal and sublethal levels, and, thus, is suggested to be an acceptable surrogate for use in risk assessment.

A long-term ichthyoplankton monitoring program suggests climate-induced environmental variabilities changed fish communities in the Hudson River estuary

“…For freshwater species, we hypothesized that the species richness in the lower HRE would decrease with changed salinity gradients due to spatial avoidance (i.e. ability of organisms to detect and move away from a stressed environment, Venancio et al, 2020;Venancio et al, 2021); while the freshwater species richness in the upper HRE was hypothesized to increase due to displacement of the freshwater species in the lower HRE. To further examine other aspects of species' diversity, we used species evenness which incorporates richness as well as species' abundance for both life stages in upper and lower HRE.…”

Wild Plant Habitat Characterization in the Last Two Decades in the Nile Delta Coastal Region of Egypt

“…Habitat destruction is one of the major threats facing plant species conservation throughout the world. In the Nile Delta, urban crawling and seawater intrusion are the primary threat to the survival of wildlife [1]. When an ecosystem has been dramatically altered by human activities such as agriculture, oil and gas exploration, commercial development, or water diversion it may no longer be able to provide the food, water, cover, and places to raise young that wildlife needs to survive [2,3].…”

“…The flora of the Nile Delta coastal land is rich in many wild plant species, which seem to be economically promising. The Deltaic Mediterranean coast is distinguished into two divisions: (1) The coastal zone, which can be subdivided into sand dunes, sand flats, salt marshes, and sandy fertile lands; (2) The shorelines of the northeastern corner of Lake Manzala [4]. On the other hand, the cultivated land habitats can be divided into: (1) Winter crops, comprising clover, wheat, broad beans, flax, and winter vegetables; (2) Summer crops, comprising rice, cotton, maize, and summer vegetables; and (3) Orchards, comprising citrus, grapes, and bananas.…”

Salinity Affects Freshwater Invertebrate Traits and Litter Decomposition

“…How freshwater organisms and ecosystem processes will respond to the increasing salinization of coastal freshwaters, predicted by the Intergovernmental Panel on Climate Change [1], is a fundamental quest for an integrated biodiversity and conservation management of coastal ecosystems at risk. Studies on a wide variety of lakes, rivers, and wetlands have shown salinity effects on freshwater organisms and on ecosystem structure and function [3][4][5][6]. Regarding freshwater animals, salinity may have lethal effects once a threshold is exceeded, or sub-lethal effects, reducing both organism and population fitness, and resulting in the decline of richness with increasing salinity [3,6].…”

“…Studies on a wide variety of lakes, rivers, and wetlands have shown salinity effects on freshwater organisms and on ecosystem structure and function [3][4][5][6]. Regarding freshwater animals, salinity may have lethal effects once a threshold is exceeded, or sub-lethal effects, reducing both organism and population fitness, and resulting in the decline of richness with increasing salinity [3,6]. Salinity also affects organisms' spatial distribution, trophic and other interactions, biochemical cycles, and leaf litter decomposition (e.g., [3,[7][8][9]), thus altering ecosystem structure and function.…”