King County lake habitat
The natural biodiversity of the lakes of King County is strongly influenced by geography. The county runs from the Cascade mountain crest to the shores of Puget Sound, covering all three different Level III ecoregions (Puget Lowland, North Cascade, and Cascade). The geology, elevation, climate, and ecology in these three ecoregions are all different, and these differences in environmental factors determine the natural biodiversity of the lakes and also influence the risks, vulnerability, and impacts to that biodiversity.
All of King County below 305 meters (1,000 feet) elevation is in the Puget Lowland ecoregion and has just over 1,000 lakes and ponds. Similar to the high mountain lakes, the lowland lakes were formed during the last glaciation. Most of the smaller lakes are recessional outwash lakes, and the two largest lakes, Sammamish and Washington, are semi-fjord like lakes gouged out by the glacial advance. Most of these lowland lakes are shallow and small with only 50 of them greater than 1 hectare (2.5 acres) in size and only 7 greater than 100 hectares (247 acres). The Puget Sound ecoregion also has the highest density of human population and development pressure in the State.
Lake Washington is the largest lake in King County and the second largest lake in Washington, and it provides one of the most dramatic examples of human impacts on the biodiversity of lakes. In 1916 a Ship Canal was opened between the Lake Washington (via its connected Lake Union) and Puget Sound, and the plumbing of the lakes drainage system changed from discharging through the Black River at the southern end of the lake to discharging ten miles north though the Ship Canal and locks. These modifications decreased lake elevations by nine feet, changed flow patterns and the time water stays in the lake, and promoted shoreline development and industrial activity, particularly around Lake Union. The sediments in Lake Union have been degraded by these activities such that there is little benthic fauna left in the lake.
The historic degradation of water quality in Lake Washington from increased population, development, and effluent discharge into the lake and the lake’s subsequent recovery after the removal of sewage effluent is one of the best known examples of pollution and recovery of a large lake anywhere in the world. These and other modifications have had significant impacts on the biodiversity of Lake Washington. Some of the most dramatic and therefore best known impacts are the alteration of the phytoplankton population from an oligotrophic high-clarity low-productivity community, to a eutrophic high-productivity cyanobacteria-dominated ‘Lake Stinko’ of local media fame, and back to the mesotrophic lake phytoplankton community enjoyed today. This phytoplankton shift resulting from human-caused changes in nutrient loading in the lake resulted in documented modifications to the zooplankton and fish communities. Current research is focusing on how picoplankton and nanoplankton (the really little algae) determine how the lake’s ecosystem functions. Very little data exists on the current populations of these small plankton, but changes in the water quality over the past 100 years have probably had impacts on the biodiversity of these communities as well. How these changes translated into impacts on higher trophic levels and the overall biodiversity of the lake is impossible to determine with the data we now have, but it is a good assumption that impacts occurred.
On the other end of the size scale from nanoplankton, there have been numerous manipulations of the vertebrate, invertebrate, and plant assemblages in the Puget Sound lowland lakes, even greater than introduction-caused impacts in the alpine lakes. The current fish assemblage in Lake Washington has multiple established populations of non-native fish species that were officially and unofficially introduced to the lakes by state agencies, anglers, and private citizens. To name only a few, carp, perch, large and small mouth bass, weather loach, corbicula clams, red swamp crayfish, goldfish, neomycid shrimp, American bullfrogs, mute swans, nutria, Eurasian milfoil, elodea, and hydrilla are all non-native species with currently established populations in King County lakes. Every exotic species that is introduced into the native ecosystem has impacts and repercussions up and down the trophic ladder. Introduced non-native species represent the greatest current threat to the biodiversity of King County lakes. It is assumed that new introductions will continue to occur and how they will impact our lakes is unknown. These impacts to the biodiversity of the lowland lakes is probably mediated by the size and productivity of the lakes, similar to what is observed in the alpine lakes, but here too additional studies needs to be conducted to gain a better understanding.
In the North Cascade and Cascade ecoregions, which together comprise the mountainous eastern half of King County, a majority of high alpine lakes appeared with the recession of the last glaciation around 13,000 to 17,000 years ago. In the North Cascade portion of King County, north of Snoqualmie Pass, lies an area of lakes formed from glacial scouring. These lakes sit in rock basins, mostly between 1,000 metes (3,300 feet) and 1,830 metes (6,000 feet) in elevation. Some reside in steep-sided cirques where snow and ice accumulate to great depths and the lakes may remain frozen well into summer. These lakes tend to have the deep azure color characteristic of high alpine lakes. Other lakes occupy broader basins surrounded by alpine forest and meadows. Two-thirds of the Alpines Lakes Wilderness is in King County, and 490 lakes are in the county’s portion alone. Of those, 193 are 4 hectares (10 acres) in size or larger. These areas were explored well before the turn of the 20th century as miners and railroad surveyors penetrated the wilderness in search of ore and routes. Their trails have been adapted by hikers to gain access to the alpine areas after they were abandoned by miners.
As a result of the mountainous topography, elevation, and isolation, many of these lakes were not naturally colonized by fish after the glacial retreat. Instead, many species of amphibians and frogs found relative safety in these fishless lakes for breeding. By the early 20th Century, however, federal, state, and county agencies were stocking many of these wilderness lakes, including the small high-elevation lakes, primarily with non-native brook trout, rainbow trout, and cutthroat trout. Although the fish stocking of many of these lakes provided excellent recreational opportunities, the introduction of a top predator into an ecosystem where it did not co-evolve had significant impacts on the biodiversity of these alpine lakes. Many of these lakes have seen alterations in the populations of macroinvertebrates and of native amphibians, such as the long-toed salamanders. Alterations at these trophic levels are assumed to create a cascading effect though the ecosystem of the lakes. How strong the impact of non-native fish introductions is on the native biodiversity appears to be dependant on the size and productivity of the lake, with the impacts apparently dampened in larger more productive lakes. What the thresholds for these effects are has not been clearly defined, nor is it known how quickly the biodiversity of these lakes can recover, or if recovery will occur after the removal on non-native fisheries. Currently, the impact of fish introductions into high lakes that did not have native fish populations is being studied, and stocking has been suspended in many of these lakes in the North Cascades National Park (outside of King County to the north). The suspension of fish stocking in lakes that did not have native populations is also being considered for the Alpine Lake Wilderness area in King County.
Another threat to diversity is the impact to our lakes from global climate change. We are already seeing some signals of local climate change in our lakes in modification of the timing and duration of thermal stratification and in the reproductive cycles of zooplankton. What long term impacts these thermal modifications will have is not definitively known, but there is no debate that if temperature increase, the probability of maintaining, let alone recovering, our native salmonid runs will be in serious jeopardy. If our streams and the surface waters continue to warm, the cold bottom waters of lakes Sammamish and Washington may provide a thermal refugia for cold water species, but only if we can protect water quality sufficiently to maintain adequate concentrations of dissolved oxygen. Low summer dissolved oxygen in Lake Sammamish and some of the smaller lakes that thermally stratify decreases the portion of these lakes capable of serving as thermal refugia. The low dissolved oxygen in the bottom of the lake is a result of the increased productivity in the lake as a response to non-point loading of nutrients and increased primary productivity. These problems makes the protection and the improvement of the water quality in these lakes as important as ever.
Protection of the biodiversity of the lakes in King County depends on protecting the biodiversity of our local rivers, streams, and wetlands. This local effort will not be successful if it is not coupled with a broad-scale approach to correcting activities that decrease the biodiversity of these waterbodies. Reducing pollution and protecting water quality is a local and regional issue, and to succeed needs to be coupled with a global effort to control the spread of exotic species and address the impacts of global climate change.
