ESTUARY TYPES AND PROCESSES

Module 1

What is an estuary?

Definition is difficult. Classified by physio graphical parameters ie: geomorphology and hydrology only early definition (Cameron and Pritchard, 1963) an estuary is a semi enclosed coastal body of water having a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage

 Four major elements i) its a coastal feature, ii) it has provision for salt water, iii) the salt water must be measurable, iv) fresh water is derived by rivers. Excludes tides

 Dalrymple et al. (1982) a new geologically-orientated definition the seaward portion of a drowned river system that receives sediment from both fluvial and marine sources and contains facies influenced by tide, wave and fluvial processes. The estuary is considered to extend from the inner limit of the tidal facies at its head to the outer limit of coastal facies at its mouth.

Classification by tidal range (Hayes, 1975) Micro-tidal estuaries Meso-tidal estuaries Macro-tidal estuaries Evolutionary classification (Dalrymple et al., 1992) Wave dominated estuaries Tide dominated estuaries Morphological classification (Fairbridge, 1980) Seven types

ESTUARIES
Comprise 5% of Earths surface, but only 2% of ocean volume; However ~60% of world population Estuaries amongst most populated areas in world For transport, industry, residence, and recreation. Estuaries have high biological productivity

 High level of food production Coastal waters supply ~90% of global fish catch. Human activities - sedimentation from cleared land, over fishing/trawling, destruction Wetlands, eutrophication, pollution, dams, canals and dykes for flood protection Dynamic systems associated with river mouths

 Estuaries are tidal, lower part of rivers and associated valleys Distinction difficult consider it a continuum of delta estuarine landforms Processes function of catchment and receiving basin Balance of wave, tide and river exerts control over morphology and evolution.

Deltas Shore-line protuberances River supplied sediment accumulates faster than redistributed By waves, currents and tides Affected by tidal dynamics, mixing of fresh & saline waters

Estuaries Seaward part of drowned river system receiving fluvial & marine sediment Influenced by tide, wave, fluvial processes. Comprises fluvial-dominated upper section - marine-influenced lower zone - central mixed region.

Tide-dominated estuaries Macro tidal Dominated by tidal currents On pro-graded coastal plains Funnel shaped, wide entrances Well mixed due to strong bi directional tidal currents Rapid flows re-suspend & transport sediment

 Three zones - upstream river dominated, - central mixed energy zone - seaward marine dominated Central zone area of sediment convergents river and marine processes

Wave-influenced estuaries Enclosed or partly enclosed behind wave built sand barrier On wave dominated coast Separated from open ocean by sand barrier Inlet intermittently closed Gradation to coastal lagoon may be permanently or intermittently open Decrease in water area and depth with time due to: - input of sand from shelf - extension of fluvial deltas from rivers - vertical accretion of mud in central estuary

 Sedimentation rates in central mud basins ~1mm/yr Along NSW coast - different stages of infill Tidal range attenuated by narrow entrance

Coastal lagoons
Features: i) shallow where salt and fresh water interact, ii) water impounded by some type of sedimentary barrier and, iii) connection with sea restricted Aligned parallel to coast, separated by barrier Impounded by sand barrier Low salinity

Morphological definition of estuaries (Roy 1982, 1984) Three types of estuary on basin morphology & condition of seaward entrance - Type 1: Drowned river valley estuary - Deep, open ocean entrance, full tidal range - Type 2: Bay Mouth Barrier Estuary - Narrow entrance, attenuated tides - Type 3: Saline Coastal Lake/Lagoon Closed entrances All have central basin

Type 1 drowned barrier estuaries sub aqueous flood tide delta extensive fluvial delta & channel fill sequence

Type 2 barrier estuaries Due to shallow valleys Marine-sourced sediments have considerable sub aerial expression ie barriers, spits, & wash over flats Landward portion terrestrially derived forming network of delta distributory mouth bars, medial channel bars

Type 3 coastal lakes Relatively small barriers, beaches & wash-over fans Flood tide deltas poorly developed or absent Fluvial deposits consist thin wedge of sandy delta & flood plain deposits mantling peaty muds of central lake - dominant facies Estuaries evolved from one type into another Sometimes a continuum.

AUSTRALIAN ESTUARINE AUDIT (Oz estuaries) Of 979 estuaries, >40% small catchments (<15km2).

Value of estuaries (NLWRA, 2002). Middens of Indigenous Australians shellfish and fish bones Sydney Harbour middens >40m high For transportation, agricultural manufactured goods Ports, shipping, industry, agriculture, tourism, residential development Human-made capital and natural capital

Natural capital - habitat, sporning, nursery environments for fish Habitats & breeding regions for birds, and marine animals Nutrient cycling Provide natural buffer between land & ocean Salt marshes and mangroves Sediment and nutrient filtration by trees, salt marsh & other wetland flora

Human capital - natural assets Sheltered deep water for shipping, industry & urban development Detrimental influences on natural assets Fisheries critically dependent on environmental status of ecosystem Survival of commercial activities dependent on disturbance Commercial fishing in Australian estuaries ~$0.4 b/y Prawn fisheries, oyster farming, barramundi & mud crab fisheries

 Estuary-dependent fisheries are fish and crustaceans spend part of life cycle in Estuarine environment i.e. estuary a nursery area. Estuaries worth ~$40 m/yr NSW oyster industry worth ~$29m 1999/2000 Productivity 1997 to 2000 declined by 350 t due to poor estuarine condition Prawn production north NSW worth $107m 1999/2000

 Production declined 8912 t in 1997/1998 to 5605 t 1999/2000 Catch declined 1800 t from Qld and NT to ~600 t recreational catch $3.6 m. Commercial crab production in 1999/2000 - $42.3 m Qld, NSW, SA, WA and NT. Recreational fisheries in Aust $2.9 b/y with >60% in estuaries (i.e. $1.7 b)

Port infrastructure (NLWRA, 2002). Port Melbourne, largest port in Aust, handles $50 b/y Trade Qldss ports >$14 b/y Marine-based tourist industry from Aust ports >$5 b/y

Australian Estuaries Audit (NLWRA, 2002) Classified by process, type and condition. Six sub classes relative to wave, tide and river energy to control geomorphology Includes drowned river valleys, embayments, small coastal lakes, lagoons and creeks. About 40% total estuaries strand plains & tidal creeks due to low river discharge low relief.

Stage 1: Assessment Australian near-pristine estuaries. Provided cost effective basis to focus management These estuaries require improved understanding of processes to provide conservation & management strategies.

Summary of condition
50% near-pristine, 22% largely unmodified, 19% modified and 9% extensively modified.

Key pressures identified by Audit 1. Excess nutrients From decaying plant & animal material, eroded soil, sewage, industrial discharge, storm water run off, fertilizers, garden waste, agricultural run off. 2. Sedimentation Fine grain sediments from catchment & near shore marine sands important Excess sediment associated with nutrients, toxicants, and pathogens Catchment erosion caused by vegetation clearing & land use practices Sediments may bypass estuary.

3. Habitat loss Shallow sandy flats, sea grass beds, salt marshes, mangroves and wetlands influenced by drainage, land clearing & dredging activities.
4. Changes to flow and tidal flushing Construction of dams, removal of fresh water increased sedimentation, shell fish survival and impact fish reproduction.

5. Pathogens and contaminants Sources human and animal waste, sewage and stormwater, contaminants associated with industrial discharge, agricultural run off, shipping and stormwater. 6. Introduced pests Introduction of exotic biota result in ecological & economic impacts. May destroy native populations; degrade habitats, effect fishing, boating, swimming. 7. Modifications to ocean entrances Artificial entrances impact estuarine ecology e.g. larval recruitment & export to & from estuary.

SEDIMENT TRANSPORT PROCESSES

Modes of sediment transport Three transport modes - wash load, suspension & bedload within a continuum Wash load - finest fraction, clay particles kept in motion by turbulence Suspension by erosion of sediment of estuary bed Grain size <150mm

 Grains >150mm move as bedload Initially grains move by saltating Reversal of current velocities give periods of slack water, suspended material settles

Mud, silt and sand (Wolanski, 2007) Cohesive sediment mean particle size <4m Non-cohesive sediment mean size >62.5m Silt is 4-62.5m Mud & sand transported in water column by different processes Sand carried mainly on bottom, mud in suspension Suspended particulate matter (SPM) comprises sediment & biological matter

PHYSICAL, CHEMICAL, BIOLOGICAL AND ANTHROPOGENIC PROCESSES CONTROLLING CONTAMINANT BEHAVOUR IN ESTUARIES Physical partitioning is grain size, surface area, specific gravity, magnetic properties Chemical partitioning refers to separation, identification & quantification chemical components Physical & chemical factors strongly interrelated.

A 1, 2 B 1, 2 G 1, 2

D E

A. B. C. D. E. F. G. H.

Atmospheric deposition 1. wet, 2. dry Fluvial inflow 1. particulate 2. dissolved phases Permanent burial Benthic diffusion Resuspension Resettlement Export 1. particulate 2. dissolved phases Absorption/desorption

ESTUARINE PROCESSES
Inputs of metals to estuary Stormwater: Fluvial discharges to estuary for dissolved & particulate heavy metal phases High- and low-precipitation conditions Stormwater most important point source of heavy metal contaminants to estuaries

Atmospheric deposition: Atmospheric metal contributions to estuary by direct deposition & indirectly via the catchment. Leachates from reclaimed lands: Original area of estuaries reduced by reclamation of intertidal areas using domestic/industrial waste & contaminated estuary sediments High dissolved metal-release rates measured in laboratory leachate column experiments using simulated rainwater and seawater percolating through field infill material Metal measured in leachate from reclaimed lands

Benthic diffusion: Calculated from core data & from analyses of pore water Metals tightly bound in bottom sediment by sulfides, metal influx insignificant.

Export of metals from the estuary

Permanent burial: Sediment surface layer (hydrous layer)(top 20cm) interacts with water column through resuspension Underlying sediment physically isolated from overlying water Underlying sediment is a chemical sink

Contaminant export under low- and high-precipitation conditions for stratified estuaries: During dry weather, small supply of stormwater mixes with saline water close to entry points Particulates flocculate out of water column & dissolved forms adsorb to particles Main water body well mixed at, or close to normal sea water salinity throughout waterway Particulate-dissolved metal phases stable over periods of weeks in main water body Under these conditions marine export negligible

 During high-precipitation, stormwater rapidly enters estuary as discrete, buoyant layer of high-turbidity water ~1m thick & moves quickly down harbour exits estuary Density differences between salt & overlying freshwater during rainfall events retard mixing & promote seaward transport

 Plumes provide mechanism for contaminants

("first flush") to bypass estuary -dispersed at sea Settling rates under these conditions minor Settled matter metal concentrations low with minimal mixing along boundary layer in upper estuary