Lake George. Chief concerns as revealed by science

Transcription

1 Lake George Chief concerns as revealed by science

2 The State of the Lake f e w other lakes of compa r a b l e size and lat i t u d e have been so little altered by humans as Lake George, a result of geography and ongoing efforts to protect one of the world s natural treasures. Situated within the Adirondack Park and surrounded by forestlands, Lake George has been largely insulated from environmental threats that have seriously degraded lakes elsewhere. Preservation of outstanding drinking water and recreational opportunities has also made the lake uniquely valuable as a scientific resource. Given its special status, Lake George served as the reference clean lake for the National Science Foundation s International Biological Program during the 1960s and 1970s for studying effects of pollution in lakes elsewhere. But Lake George is not entirely shielded from threats, with clear signs of stress on the lake s ecological health and natural resilience now revealed by latest research. Primary concerns stem from invasive species that disrupt the ecological functioning of the lake, and from excessive loadings of salt and of nutrients like phosphorus and nitrogen that stimulate plant and algae growth and can degrade water quality if left unchecked. Also, intentional introductions of fish species that were never part of the lake s natural fish community, especially rainbow smelt, Our understanding of Lake George comes from 30 years of data may be having subtle adverse effects on the lake s ability 1 collection and analysis, done in conjunction with RPI s Darrin Fresh to support recreational fishing. Together these stresses Water Institute. Chief concerns about the state of the lake are highlighted here in this document. If you d like to dig deeper into the have multiple and interacting effects on the lake. science, view the full report at our website: fundforlakegeorge.org/stateofthelake One of the world s clearest, cleanest large lakes within a densely populated region.

3 THREE PRIMARY THREATS HOW THESE THREATS INTERACT 1 3 INVASIVE SPECIES Five species including spiny waterflea, asian clams, zebra mussels, curlyleaf pondweed, and Eurasian watermilfoil, that aggressively adapt to lakes like Lake George and can dramatically alter how they function ecologically. RISING SALT LEVELS Thirty times above the natural background and increasing fast, from roadway de-icing applications during winter. Among other impacts, salt will make the lake s water unsafe to drink for some people within a few decades if loadings aren t curtailed. DECLINING WATER QUALITY AND CLARITY Measurable (about 6%) loss of clarity, an indicator of declining quality, caused by either or both: Increased discharges of plant fertilizers, stormwater runoff, and wastewater adding phosphorus and nitrogen that stimulate microscopic algal growth in the water, decreasing light penetration. Introductions of alien forage fish species like rainbow smelt that consume microscopic animals that would otherwise eat the microscopic plants, allowing the plants to proliferate. Introduced species may be having compound effects on ecosystem health. Increased nutrient loading makes it easier for invasive species to become established in the lake. Rising salt levels change how nutrients enter into, and circulate within, the lake. Increasing microscopic algae may lead to an ecological tipping point that could dramatically and irreversibly reduce water clarity. This primer on lake health details the key threats facing Lake George. Thorough review of 30 years of data and analysis can be found in The State of the Lake report: fundforlakegeorge.org/stateofthelake. The Fate of the Lake: A Blueprint for Protection available at fundforlakegeorge.org/fateofthelake describes The FUND s integrated commitment to addressing these threats and securing the health of Lake George for the next generation. 1 INVASIVE SPECIES Aquatic invasive species are a mounting threat to Lake George that has attracted growing concern basin-wide. The escalating cost of invasives treatment and control is enormous, and the impacts of infestation can be severe from degraded water quality and recreational opportunities to declining tourism revenues and property values. Currently, Lake George has five aquatic invasive species, including: two aquatic plants, Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogetum crispus); two mollusks, zebra mussel (Dreissena polymorpha) and asian clam (Corbicula fluminea); and one crustacean, spiny waterflea (Bythotrephes longimanus). 184 ST. LAWRENCE RIVER The escalating cost of invasives treatment and control is enormous. As depicted here, neighboring waterways possess dozens more aquatic invasives: Great Lakes, 184; Lake Champlain, 49; the Hudson River, 91; the St. Lawrence River, 87; and the list only grows longer. Clean Boats Only, The FUND s groundbreaking report on the invasives threat and its solution, features coming soon? species of greatest concern to Lake George, including water chestnut (Trapa natans), hydrilla (Hydrilla verticillata), and quagga mussel (Dreissena bugensis). The close proximity of these neighboring threats is alarming. Aquatic invasives hitchhike on boats, trailers and other equipment, making people unsuspecting carriers as they travel from one waterbody to the next. Moreover, invasives, particularly in their juvenile form, can easily escape detection. Prevention provides the only 3 4 GREAT LAKES NUMBER OF INVASIVE AND NON-NATIVE SPECIES IN NEIGHBORING BODIES OF WATER DATA SOURCE: UNIVERSITY OF VERMONT, LAKE CHAMPLAIN SEA GRANT, GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. LAKE CHAMPLAIN 5 HUDSON RIVER LAKE GEORGE 91 real (and affordable) means of protecting Lake George, and other vulnerable waters, from the gathering invasives threat.

4 RISING SALT LEVELS The most obvious trend documented in The State of the Lake report is a relentless rise in salt concentrations. Salt is being called the acid rain of our time with good reason. Each year, 8,000 metric tons of road salt (and another 6,000 tons of sand) are applied on basin roadways during winter, an estimated 13 tons per lane mile. Much of the salt eventually drains into the lake and is beginning to affect how the lake functions both physically and biologically. Salt levels have tripled since 1980, and are more than thirty times above the natural background characteristic 3 DECLINING WATER QUALITY AND CLARITY Measurable loss of clarity is almost certainly caused by increasing phytoplankton, microscopic plant-like algal organisms that absorb and scatter light in the lake s surface waters. Phytoplankton abundance has increased by about 33% throughout the lake, mainly during summer and early fall. The phytoplankton increase is most likely the result of greater nutrient loading, especially of phosphorus. This loading ultimately comes from increasing intensity of development in the Lake George Basin, generating more wastewater treatment discharges, using more lawn fertilizers and more household detergents, and intensifying stormwater runoff, all of which contain phosphorus in forms that can be used by phytoplankton to spur growth. EXCESSIVE ALGAE GROWTH Another factor that may contribute to greater phytoplankton abundance is the introduction of rainbow Phytoplankton abundance of Adirondack lakes in smelt to the lake. Introduced in the early 0th century to has increased by about provide more forage fish for salmon and trout to eat, the undeveloped watersheds. rainbow smelt population became self-sustaining by the 33% throughout the lake, late 1970s. The increasing abundance of rainbow smelt caused an unexpected shift in the lake s zooplankton, the most likely the result of microscopic animals that feed on phytoplankton. Rainbow smelt consume the larger zooplankton species more greater nutrient loading. efficiently than the native fish community in the lake, and larger zooplankton species consume phytoplankton more efficiently than smaller zooplankton. The result is less phytoplankton being consumed, allowing the abundance of phytoplankton to increase. Rainbow smelt may have 5 SCHOOL OF SMELT 6 Salt levels have tripled since 1980, and are more than thirty times above the natural background characteristic of the efficiency of the food web that produces the animals reduced the lake s carrying capacity for fish by reducing Adirondack lakes in undeveloped watersheds. If allowed rainbow smelt and other forage fish prey on. to continue rising at the current rate, within the next one to two decades, the lake s water the primary source of Any addition of phosphorus will stimulate algal growth in drinking water in the basin will become a health hazard the lake. In addition to the phytoplankton in the surface to people suffering from hypertension. Present salt levels waters offshore, this includes macroscopic algae that grow are starting to affect how water moves within the lake; on the lake bottom near shore, and also the Nitella meadows macroscopic algal plants supporting a distinctive when, where and how nutrients are introduced to the lake; and the make-up of microscopic plants and animals branch of the lake s food web that grow on the bottom that support fish. These trends raise serious concerns. of the lake at deeper depths.

5 NITELLA MEADOWS Hidden from view but ecologically crucial, Lake George hosts extensive meadows of Nitella. These meadows grow on soft bottoms of the lakebed at depths of 0 to 50 feet where currents are weak, with individual plants attaining lengths of five feet or more. Covering about 15% of the lakebed in the north basin and 0% in the south, Nitella meadows account for 30% of the total plant production of the lake. This productivity of Nitella supports a complex food web, with caddisworms, mayfly nymphs, freshwater shrimp and other invertebrates grazing on the Nitella plants, to be consumed, in turn, by juvenile and adult fishes including smallmouth bass, yellow perch, bullhead and lake trout. Dense networks of Nitella also provide cover where juvenile fish can hide from predators. The Nitella meadows thus play a vital role in sustaining the fish community in Lake George, and thereby recreational fishing. The Nitella meadows help maintain the water clarity on which they depend for light to grow. But this very dependency makes the Nitella meadows ultimately vulnerable to excessive nutrient loading to the lake. While Nitella meadows reduce the response of phytoplankton to increased nutrient loading, they do not eliminate it. Left unabated, excessive nutrient loading could reach an ecological tipping point where shading from the increased phytoplankton causes the Nitella meadows to decline, making more nutrients available to the phytoplankton. As illustrated below, once engaged, this negative feedback loop could lead to an abrupt decline in water clarity that would be very difficult to reverse once light penetration to the depths where Nitella thrives is inadequate to support growth. Because so many of the lake s fish and other animals depend on the Nitella meadows, their loss could dramatically alter the fishing and ecological functioning of the lake, probably irreversibly. The Nitella meadows thus play a vital role in sustaining the fish community in Lake George, and thereby recreational fishing. PHYTOPLANKTON Nutrient loading could reach an ecological tipping point where shading from the increased phytoplankton causes the Nitella meadows to decline. Given the key ecological role of the Nitella meadows, monitoring their size and health is a high priority for early detection of adverse changes from nutrient loading in the lake. As long as the meadows remain intact and healthy, the effects of nutrient loading will remain relatively subdued. Knowing that the lake is extremely sensitive to increased phosphorus loading, and that the shading from the phytoplankton response could lead to a sudden decrease in water clarity, sustained vigilance will be required to avoid this outcome. Measures described in The Fate of the Lake are designed to safeguard the lake s delicate ecological balance. Most aquatic plants in Lake George receive inorganic nutrients like phosphorus and nitrogen needed for growth through their roots from lake bed sediments. But Nitella can absorb these nutrients directly from the water column, so they compete with the microscopic phytoplankton that float in the surface waters. This compe- 7 tition limits how much the phytoplankton can increase Phytoplankton thrive on 8 in response to excess nutrients added to the lake from increased phosphorus from 4 human development because a substantial portion of the runoff. nutrients instead go into the growth of Nitella. By reducing the number of microscopic phytoplankton particles 3 As phytoplankton grow, that absorb and scatter light in the lake s surface waters, sunlight for Nitella is reduced, the Nitella meadows help maintain the water clarity on threatening Nitella s survival. RAINBOW SMELT which they depend for light to grow. But this very dependency makes the Nitella meadows ultimately vulnerable to 4 excessive nutrient loading to the lake. ZOOPLANKTON 1 3 NITELLA 1 Rainbow smelt feed on zooplankton, the main consumer of phytoplankton, allowing the phytoplankton population to grow. Since Nitella consume phosphorus, as the meadows recede, there is more phosphorus to promote phytoplankton growth.

6 COMPOUNDING STRESSES Because of its relatively healthy condition overall, Lake George retains considerable capacity to respond to changes while still functioning more or less the same ecologically. Lake George has coped with alien fish species deliberately introduced to the lake, along with overfishing, for more than a century. In fact, the first rigorous biological survey of the lake in the early 190s was aimed at reversing the decline of fishing. But at some point, external stressors imposed too quickly or for too long can prompt a drastic reorganization of the food web and undermine lake health. Avoiding such tipping points is the primary goal of enlightened management. Success requires a clear understanding of how stressors independently and in combination threaten the lake s ecological stability. THE FATE OF THE LAKE PHOTO BY CARL HEILMAN II External stressors imposed too quickly or for too long can prompt a drastic reorganization of the food web and undermine lake health. The primary stresses on Lake George invasive species introduced inadvertently; salt loading from winter roadway de-icing; nutrient loading from excessive fertilizer use, household detergents, wastewater treatment and stormwater runoff; and numerous fish species such as rainbow smelt deliberately introduced to the lake to improve fishing have not yet changed how the lake functions fundamentally. However, certain trends underway, such as increasing phytoplankton growth stimulated by nutrient loading, and accompanying declines in water clarity should be taken as warning signs. These signs require prompt attention and trend changing actions to secure the natural beauty and wonder that make Lake George Lake George. Unconstrained increases of nutrients could eventually lead to the loss of the lake s Nitella meadows, followed by a much more substantial decrease in water clarity and increase of nuisance algae. Fish stocking programs have often been suggested or implemented with scant regard for the lake s inherent capacity to support them, and in the case of rainbow smelt, may have actually reduced this capacity. Doubling the salt concentration from its current level would threaten the lake s safety as a source of drinking water for people suffering from hypertension, not to mention the adverse impacts of salt increases to lake health. Most threatening of all, invasive species can quickly and radically alter the kinds and population sizes of species throughout the lake s food web. The bold actions recently taken to prevent invasive species from wreaking ecological havoc on Lake George provide a strong platform for taking on these other stressors with the same intensity and diversity of commitment. the problem with identifying ecological tipping points is that they are too often elusive and hard to predict. Once triggered, the cascading impacts are even harder, and many times impossible, to reverse. Hence, understanding the state of Lake George and the stressors on lake health place us in the enviable position of heading off calamitous change before thresholds are reached that foreclose preventive measures. The priority is particularly acute in the face of climate change, where lake temperatures have already increased by 3. degrees Fahrenheit since Strengthening the lake s ecological resilience to external stressors beyond our immediate control is a powerful incentive for concerted action on those issues where we can make a difference. Moreover, like the remarkable strides already made in stopping invasives, this work can inform and inspire others facing the same challenges. In the companion volume, The Fate of the Lake: A Blueprint for Protection available online at fundforlakegeorge.org/fateofthelake specific measures are prescribed that build upon progress in holding back invasive species. As for invasives, these measures apply the three pillars of The FUND s Legacy Strategy unprecedented partnerships, program innovations, and direct investments all arrayed to fulfill the Strategy s driving goal: stopping the present decline of water quality and achieving sustained protection for the next generation. A bold new commitment to science through The Jefferson Project at Lake George The FUND s historic partnership with IBM and RPI will monitor progress as it opens new doorways to lasting success. Once triggered, the cascading impacts are even harder, and many times impossible, to reverse. Strengthening the lake s ecological resilience to external stressors beyond our immediate control is a powerful incentive 9 10 for concerted action on those issues where we can make a difference.

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