Today: Coastal Issues and Estuaries Coastal issues Human effect on coastlines What is an estuary Why are they so important? Circulation of water in estuary Environmental issues Coastal Issues: Problem with Beaches People like em Try to keep them Try to protect investments Problem: Ocean is more powerful than we are. 1
Attempts to protect beaches from erosion usually cause problems! Expensive & Unsuccessful Hard stabilization of beaches Attempts to protect beach from erosion Groins, Jetties and Sea Walls Groins and jetties (perpendicular to the beach) Trap longshore transport of sand. Starve down-current beaches of supply (causing erosion) Seawalls Intended to prevent erosion of beach Increase wave E at base of wall causing erosion in front of wall (Miami)! Replenishment EXPENSIVE Fine sand washes away Groins & Jetties Trap beach drift & Longshore current (bars) Starve down current beaches (erosion) 2
Breakwater at Santa Monica CA disrupted the longshore transport 3
Miami Beach Largest beach replenishment project in US Began in 1981, cost 60 million $ Slow rate of erosion keeps sand on the beach In places the beach has eroded despite groins and replenishment. Seawalls built to protect property. Now, no beach at all! Carolina Beach Replenished beach in 1986 at great expense to NC and USA Two years latter the beach was gone! One good storm and all that sand was moved offshore. 4
Btw: what s an unusual storm? Any storm that destroys the beach! Ultimately, all stabilization efforts fail. Replenishment will always fail, because the coast is removing the beach for a reason. Storms and natural variations change the character of any beach. We try to stop this change to protect or preserve the beach. Doing so cost lots of money, is temporary at best, and damages the sediment circulation along the entire coastal circulation cell. Do you see the cycle? Additional problem: Jersey shore Rising sea level is going to impact coastal communities. If we try to stop the loss of beachfront property, we risk loosing the beaches altogether! 5
Issue: trapping sediment on the beach starves the circulation cell and reduces the size of beaches along coastline. Beaches: Let them Be & all will be good! This is what we have learned in the past few decades. Unfortunately, urban planners have not learned the lesson. Sometimes bad things happen, even to natural beaches. This beach will recover. It may move on-shore as sea level rises, it may move down-shore, but it will recover. The houses will not. If a seawall had been constructed prior to the storm, then the storm might ve permanently damaged the beach. 6
Sea level is rising! What do we do? We could retreat, and allow the beach to move on-shore. Or, we can stand and fight the ocean, ultimately loose, and then retreat. A Bigger Issue Body of water partly enclosed by land & replenished by river Include wetlands & marshes Protected from waves, storms by land enclosure Highest primary productivity of all marine environments Nutrient input from river & recycling from circulation Crab, clams, oysters, shrimp, fish Juvenile stages thrive Many species reproduce here Civilization too (Tigress, Euphrates, Nile, Po) Estuaries: 7
Types of Estuaries (Sounds): Drowned During glacial maximum - rivers channels move onto shelf Flooded now that sea level is high Fjords glacial cut valleys Sill or moraine at lip of estuary protects fjord from open ocean Bar - Built Spit or bar encloses bay Tectonic Plate motions (faulting) blocks sound Chesapeake Bay Susquehanna River Potomac James River Chincoteague Bay, MD St. Lawrence Columbia River Puget Sound Delaware Bay Pamlico and Albermarle Sounds Drowned Estuary 8
Fjords Bar Built Estuariess Albermarle Sound NC (Neuse and Tar rivers) Pamlico Sound, NC (Chowan R.) 9
Tectonic Estuaries Mixing Fresh & Sea Water Influenced by Estuary Shape River discharge Tidal range Restriction at mouth of sound 10
Mixing: Spectrum from well mixed to not at all Net Circulation Seaward on top of estuary (low density river water) Landward at depth (return flow of denser seawater) Result: Waste & juveniles transported to sea Nutrients & clean seawater flow into sound RECYCLING nutrients! RECYCLING nutrients: Photosynthesis at surface These organisms die and accumulate at bottom Dead organisms decompose Release Nutrients from bottom Back into land-ward flow feeding surface waters 11
Environmental Issues: Estuaries & Wetlands Should we protect them from this? Why Fisheries Self cleaning (if not destroyed): mangroves protect coast from storms, sea grass cleans toxins and metals from the water Wetlands Clean polluted water from river input - 1 acre can filter ~1/4 million gallons/year. Nurseries for >0.5 commercial fish in SE of USA Protect coastlines from storms Currently have last ~50% of wetlands worldwide Expected sea level rise this century (50 cm) cause ~40-5-% loss of existing wetlands. 12
Coastal & Estuary biodiversity declining Regional Scale A - Marked decline in number of Taxa since industrial revolution B - correlation as # species decreases, the fisheries collapse Cause: (1) water quality declining due to human activity, and/or (2) over fishing causing decline in biodiversity and this results in collapse of ecosystem. Declining Science, 2006 Extinct biodiversity of large marine ecosystems declining too (>150 k km 2 areas) Diamonds = cumulative loss Triangles = annual loss Black = all systems Blue = species- pore systems Red = species-rich systems Map shows the large marine systems color coded to fish species richness Conclusions: biodiversity of important marine ecosystems is declining. This trend will result is projected to result in complete collapse of commercial seafood fisheries by 2048. Time remains to fix this problem. Science, 2006 13
Coast video 14