Estuaries and coastal areas are dynamic zones where freshwater meets the sea. These unique environments host diverse ecosystems and play crucial roles in nutrient cycling, , and pollutant transformation.
Estuarine biogeochemistry is shaped by gradients, tidal influences, and land-sea interactions. These factors create distinct habitats like and seagrass beds, which act as biogeochemical reactors, processing and organic matter in complex ways.
Estuarine and Coastal Biogeochemistry Characteristics
Biogeochemical features of estuaries
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ESSD - Comprehensive bathymetry and intertidal topography of the Amazon estuary View original
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Top images from around the web for Biogeochemical features of estuaries
ESSD - Comprehensive bathymetry and intertidal topography of the Amazon estuary View original
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ESSD - Comprehensive bathymetry and intertidal topography of the Amazon estuary View original
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Salinity gradients
Transition from freshwater to saltwater creates dynamic mixing zone
Estuarine circulation patterns driven by density differences (salt wedge, partially mixed, well-mixed)
Salinity influences chemical reactions and biological processes (osmoregulation)
Tidal influence
Periodic water level fluctuations alter habitat availability and chemistry
Tidal flushing and water exchange transport nutrients and organisms
Intertidal zones support diverse communities adapted to desiccation and submersion cycles
Land-sea interactions
Terrestrial runoff delivers nutrients and organic matter to coastal waters
Sediment transport and deposition shape estuarine morphology and turbidity
Coastal erosion and accretion processes modify shorelines and affect habitat distribution
Unique habitats
Salt marshes and mangrove forests act as nutrient filters and carbon sinks
Seagrass beds and coral reefs provide complex 3D structure for diverse ecosystems
Mudflats and sandy beaches support benthic communities and migratory birds
Estuaries as biogeochemical reactors
Nutrient cycling
Nitrogen fixation by microbes and denitrification in anoxic sediments regulate N availability
Phosphorus adsorption to sediments and desorption under changing redox conditions
Silicon cycling in diatom-dominated systems influences phytoplankton community structure
Organic matter processing
Primary production by phytoplankton and benthic algae forms basis of estuarine food webs
Bacterial decomposition and remineralization recycle nutrients
Formation of dissolved organic matter (DOM) affects water color and light penetration
Pollutant transformation
Heavy metal sequestration in sediments through adsorption and precipitation
Biodegradation of organic pollutants (PAHs, PCBs) by specialized microbial communities
Bioaccumulation and in food webs concentrate certain contaminants
Carbon cycling
Blue carbon sequestration in coastal ecosystems (, salt marshes, seagrasses)
CO2 exchange between air and water influenced by biological activity and physical processes
Methane production in anaerobic sediments contributes to greenhouse gas emissions
Benthic-Pelagic Coupling and Human Impacts
Benthic-pelagic coupling in estuaries
Benthic-pelagic coupling
Exchange of nutrients between sediments and water column drives productivity
Influence on primary production and food web dynamics varies with depth and season
Seasonal variations in coupling strength related to temperature and organic matter input
Bioturbation
Sediment reworking by benthic organisms (polychaetes, bivalves) enhances nutrient flux
Enhanced oxygen penetration into sediments stimulates aerobic decomposition
Facilitation of organic matter decomposition through particle mixing and burrow irrigation
Sediment resuspension
Wind-driven and tidal resuspension events redistribute particulate matter
Release of nutrients and pollutants from sediments affects water column chemistry
Impact on water column turbidity and light penetration influences primary production
Benthic fluxes
Diffusive and advective transport of solutes across sediment-water interface
Role of porewater exchange in nutrient cycling, especially in permeable sediments
Importance of benthic microalgae in shallow systems for nutrient retention and stabilization
Human impacts on coastal biogeochemistry
Coastal development
Increased nutrient loading from urban runoff leads to
Alteration of natural shorelines and habitats reduces ecosystem services
Changes in sediment transport and deposition patterns affect coastal morphology
Aquaculture
Nutrient enrichment from fish farms stimulates algal growth and oxygen depletion
Introduction of antibiotics and other chemicals affects microbial communities
Modification of local food webs and ecosystem structure through species introductions
Eutrophication
Excessive algal blooms and oxygen depletion create dead zones
Shifts in species composition and biodiversity favor opportunistic species
Formation of hypoxic or anoxic zones alters biogeochemical cycling (denitrification, P release)
Climate change impacts
Sea level rise and saltwater intrusion modify estuarine salinity gradients
Ocean acidification effects on calcifying organisms (shellfish, corals) alter community structure
Changes in precipitation patterns and freshwater input affect nutrient delivery and stratification