Estuaries are the tidally influenced environments found in the transition zone between freshwater and the ocean, and are among the most productive yet fragile aquatic ecosystems on the planet. These are hydrologically complex systems, with freshwater streams and rivers flowing into coastal embayments. Because freshwater is less dense than saltwater, inflowing freshwater often “floats” on top of the tidal saltwater wedge beneath, creating a vertical density gradient. In a healthy estuary, tidal flushing can keep bottom waters oxygenated providing a great habitat for benthic organisms such as blue crabs, oysters, and flatfish.
However, waters flowing into estuaries are increasingly dominated by municipal wastewater discharges and agricultural runoff. As these nutrient-rich source waters become more quiescent in estuarine oxbows, coves and embayments, the result is often harmful algal blooms (HABs) dominated by both cyanobacteria and dinoflagellates. These HABs are often toxic, particularly to fish and other aquatic life. When these algal blooms die they settle and decompose in bottom, more saline waters. This organic loading, together with organic matter from runoff and decomposing wetland plants, can create anoxic conditions in chemically stratified bottom waters. The depletion of dissolved oxygen (DO) from bottom waters can result in the accumulation of hydrogen sulfide (H2S), which is toxic to fish, crabs, oysters and other aquatic life, and also produces the rotten egg odor characteristic of coastal marshes. Upwelling of these anoxic, toxic bottom waters (e.g., from storm events) can cause huge fish kills, noxious odor events, and provide algal nutrients to fuel subsequent HABs.
Providing enhanced circulation, SolarBees deployed in estuarine basins and canals have controlled HABs, prevented fish kills, and improved aquatic habitats. Evidence of the latter include reports of a healthier blue crab population in a Delaware inland bay, and the resurgence of an endangered oyster in a brackish water California lake. With the intake hoses set deep, SolarBees have also prevented excessive H2S accumulation in relatively deep holes.
Estuaries provide some unique challenges not prevalent in freshwater SolarBee applications, e.g., corrosion due to saltwater. However, corrosion is no longer an issue due to using 316-stainless steel for the distribution dish, pickling all welds, and employing corrosion-proof plastics for hoses, floats and other components. In fact, SolarBees have been installed in waters with salinities greater than 250 ppt without any corrosion problems. Tidal changes in water column depth are not a problem with our flexible hose technology. Dealing with high waves had been an issue (and for some large lakes as well), but that has been resolved with the “high-wave kit”, and SolarBees have survived hurricanes in Florida and Texas. Perhaps the most serious challenge has been bio-fouling, particularly with barnacles. Specialized coating, together with periodic cleaning around the time of seasonal larval production, has proven most effective.
After years of testing, learning and engineering appropriate modifications, the SolarBee is ready for estuarine applications. The ability to make a meaningful and sustainable impact will depend in great part on the hydrology of the target area, so our focus has been more on discrete inland basins, coves and bays. Please contact us if you wish to discuss the suitability of solar-powered circulation to help resolve water quality problems in your estuary.