Silica Depletion and Lake Regulation

The recent occurrence of an unusual number of “red tides” in the Gulf of Maine (“Red tide hits a rare, and frightening intensity” PPH-July 16, 2009) sparked my curiosity to ask if regulation of our inland waters was harming the ecology of our estuaries and coastal waters. For the Gulf of Maine this pattern of increasing frequency and intensity of harmful blooms began in the mid 1970s. And, it was in the mid 1970s that policies for managing flows of inland waters changed. Maine is not alone with increased freshwater flow changes and pollutants impacting the oceans so it is not surprising that, worldwide, ocean biologists have reported a worrisome recent trend in the increased frequency and intensity of harmful, poisonous algal blooms.

It turns out that one key factor associated with harmful algal blooms is dissolved silica; intense red tides tend to occur in coastal waters where dissolved silica is low. We are all familiar with nitrogen and phosphorus as nutrients fueling algae growth, but silica is also an essential nutrient for one of the most abundant algae called diatoms. Without adequate dissolved silica, diatoms can’t grow and reproduce. Much of the dissolved silica found in our State’s coastal waters can be traced back to weathering processes of Maine rocks and soils. Silica, along with other minerals, slowly dissolves and is then carried from the watersheds by rivers to the ocean. With the continuous input of silica from rivers, along with other nutrients, diatoms grow in sufficient numbers and serve to suppress harmful algae that cause “red tides”. Healthy diatom populations in the Gulf of Maine also supply the nutrient foundation for one of the historically richest fisheries in the world. Another, but more widely studied factor associated with harmful algal blooms is excess nutrients from such sources as crop fertilizers, sewage, industrial pollution, and poor land practices. Changing weather patterns, salinity and ocean currents also have relationships to harmful algal blooms. However, the excessive nutrient factor has been diminished in the Gulf of Maine, thanks to compliance with the Clean Water Act since the mid 1970’s. So what causes diminished dissolved silica? One way in which silica is prevented from reaching the ocean in a normal seasonal pattern is through disruption of freshwater flow patterns of inland lakes and rivers. Maine dams since the 1970’s increasingly function to regulate water flows for the benefit of specific recreational interests which dramatically alters the timing and volumes of freshwater flows to the ocean.

I suggest that our current management strategies of Maine dam hydrology may be an unwitting, but important factor, contributing to silica depletion, increased harmful algal blooms and the present coastal ecosystem decline. What has not been recognized in Gulf of Maine ”red tide” studies and reporting is the present degree of water flow alterations by dam regulation. Before, water flow more mimicked natural regulation and seasonal cycles due to ancient practices of wiser use of water power and flood prevention. During the 1970s decade, lake associations successfully lobbied the legislature to retain lake outflows to seasonally increase water levels of Maine’s non-hydro lakes so that shorefront owners did not have to move their docks and boaters could access shallow rivers and coves. Other flow alterations were made for guaranteeing minimum water flow in a drought or for capitalizing on changes in hydropower seasonal values. As a result on a grand scale, the timing and amounts of freshwater flows into coastal estuaries are now highly contrary to that which would occur in nature.

So, my long time interest for impacts of lake and river regulation has led me to the sea. Now I suspect that the negative impacts of fragmentation of waterways by dams and not allowing more natural flow patterns in streams extend out into the ocean where they may have dire consequences. The health of coastal diatoms has a significant impact on the earth’s carbon cycling, ocean acidification , and climate change. Considering the importance of fisheries in the Gulf of Maine and saltwater recreation to our Maine economy, scientists and environmental leaders must be encouraged to study, assess and consider the effects of the present fresh water regulation on our coastal and marine ecosystems.