Browsing by Subject "Lake restoration"

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    Effects of Aquaculture on Mine Pit Lakes near Chisolm, MN: Restoration of Twin City-South pit lake by fallowing and status of Fraser pit lake
    (University of Minnesota Duluth, 1995) Axler, Richard P; Yokom, Shane; Tikkanen, Craig A; Henneck, Jerald; McDonald, Michael E
    Net-pen salmonid aquaculture was carried out from 1988 to 1993 in the Twin City-South mine pit lake on the Mesabi Iron Range in northeastern Minnesota. A water quality controversy enveloped the aquaculture operation from its inception in 1988. In 1992 the Minnesota Pollution Control Agency mandated that all intensive aquaculture operations in the Twin City - South mine pit lake be terminated by July 1993 and that restoration to baseline (i.e. preaquaculture) conditions be demonstrated within three years. This "fallowing" has led to a rapid recovery to near baseline water quality conditions and an oligomesotrophic, i.e. unproductive, status. Water column improvement in regard to phosphorus and hypolimnetic oxygen concentrations has been particularly rapid. Although baseline conditions were not well defined for TC-S, the P budget for the lake in September and November 1994 was typical of reference pit lakes in the area. Oxygen concentrations in near-bottom water remained above 5 mg02/L in November 1994 even without artificial mixing or aeration during the 1994 growing season. Algal growth was low in 1993, as expected due to artificial mixing, and remained low in 1994 without any artificial mixing. Ammonium has been naturally converted to nitrate which is decreasing faster than expected and at a rate similar to its increase during intensive aquaculture. More rapid reductions in water column phosphorus and nitrogen might have been accomplished during the first summer by allowing the lower hypolimnion to become anoxic in order to promote denitrification and minimize sediment resuspension. The natural burial of sedimented aquaculture wastes due to high ambient rates of erosion of inorganic sediment from the basin walls has effectively minimized sediment nutrient transport to the overlying water column. Fallowing for several years appears to be an effective method for lake restoration of these pit lakes. Our data, and our analysis of the NPDES monitoring data, has shown no change in the water quality of Chisholm's drinking water source, the Fraser pit lake, attributable to aquaculture impacts. This, and no apparent change in the water quality of two nearby pit lakes, Grant and Ironworld in recent years, suggests little or no significant off-site migration of aquaculturally impacted water.
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    Limnological Re-Sampling of Chisolm Area Mine Pit Lakes with Reference to Former Aquaculture Impacts
    (University of Minnesota Duluth, 2000) Axler, Richard P; Henneck, Jerald
    Limnological surveys were conducted on two mine pit lakes (Twin City-South and Sherman) used for intensive netpen salmonid aquaculture over the period 1988-1995 and an adjacent pit lake (Fraser) used for drinking water by Chisholm, Minnesota. A water quality controversy had enveloped the aquaculture operation from its inception in 1988 to its bankruptcy in 1995. All intensive aquaculture operations in the Twin City-South pitlake were terminated in mid-1993 as mandated by the Minnesota Pollution Control Agency (MPCA) in order to determine if water quality could be returned to baseline values within three years (a condition of continued operation in the Sherman pit lake). The MPCA mandated that restoration to baseline (i.e. pre-aquaculture) conditions be demonstrated within three years. This "fallowing" led to a rapid recovery to near baseline water quality conditions and an oligomesotrophic, i.e. unproductive, status. Algal growth was low in 1993, due to light - limitation from artificial mixing, but remained low in 1994 without any management due to renewed P-limitation. Water column improvement in regard to phosphorus and hypolimnetic oxygen concentrations was particularly rapid. Although baseline conditions were not well defined for TC-S, the P budget for the lake after 18 months was typical of reference pit lakes in the area and oxygen concentrations in near-bottom water remained above 5 mg02/L without artificial mixing or aeration during the next growing season. Waste product ammonium was naturally nitrified to nitrate which decreased at a rate faster than expected, and similar to its increase during intensive aquaculture. More rapid reductions in water column phosphorus and nitrogen might have been accomplished during the first, summer by allowing the lower hypolimnion to become anoxic in order to promote denitrification and minimize sediment resuspension. Unfortunately these were precluded by the regulatory standards. The natural burial of sedimented aquaculture wastes due to high ambient rates of erosion of inorganic sediment from the basin walls effectively minimized sediment nutrient transport to the overlying water column and sediment oxygen demand.
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    The Response of Aquatic Macrophytes to Lake Management Practices and the Role of Light in the Germination of Macrophyte Propagules
    (2017-09) Dunne, Melaney
    Macrophytes are a vital component to functioning aquatic ecosystems. Specifically, macrophytes promote good water clarity by stabilizing sediments, sequestering nutrients, and reducing the abundance of phytoplankton in the water column. Also, macrophytes provide habitat for other aquatic organisms. Healthy, robust aquatic macrophyte communities are indicated by diverse, abundant stands in the littoral zones of lakes. Poor water clarity and invasive species are primary limiting factors that cause diminished aquatic plant communities. Poor water clarity reduces the light quantity, impeding the growth of macrophytes. Invasive fish, such as common carp (Cyprinus carpio), damage macrophyte communities by uprooting plants and suspending sediment and nutrients in the water column. Invasive plants, such as curlyleaf pondweed (Potamogeton crispus) and Eurasian watermilfoil (Myriophyllum spicatum), often outcompete native species creating dense monoculture stands. To improve the growing conditions for macrophyte communities, several management actions can be pursued to limit the damage by invasive species and improve the water clarity. Common management practices in Midwestern lakes include invasive species control and nutrient sequestration. These practices have been documented to enhance native macrophyte communities. Lake management often requires several years of consistent, adaptive management to effectively restore the ecosystem. Adaptive management is the systematic process of learning from past management outcomes and subsequently incorporating that knowledge into current management decisions. I evaluated the change in the macrophyte community in Lake Riley, Chanhassen, MN over the course of 6 years of lake management actions using aquatic plant point-intercept surveys from 2011 to 2016. The results of the surveys found that after a carp removal in 2010, curlyleaf pondweed dominated the littoral zone and water clarity did not greatly improve. Once invasive macrophytes were managed starting in 2013, incremental increases in the species richness of the macrophyte community occurred. However, native macrophyte expansion was limited because water clarity was still poor during the summer growing season. In 2016, after an alum treatment, water clarity improved and the macrophyte community abundance and richness further increased. Species richness increased from 9 observed species in 2011 to 15 in 2016. During peak growth in August, the native species frequency of occurrence was 50% through 2013 and then increased up to 80% of sites in 2016. The August native macrophyte biomass increased from 30g/m2 in 2011 to 600g/m2 in 2016 (p<0.05). Prior to 2016, the average maximum depth of rooted native plant growth was 3.1m and in 2016 it increased to 4.1m. Overall, the density, coverage, and richness of the macrophyte community increased throughout the study period demonstrating that the macrophyte community had a positive response to the multi-year management practices on Lake Riley. The specific mechanism of macrophyte recruitment following improved growing conditions, such as in Lake Riley, is an understudied area of macrophyte restoration. Macrophytes typically propagate through clonal growth and fragmentation. However, when macrophyte populations are reduced, the lake seed bank may contribute to the reestablishment of the population. In previous studies on temperate lake seed banks, seeds from vascular aquatic plants and spores from macroalgae have been found in varying densities and viability levels suggesting that recruitment from the seed bank is possible in some systems. I conducted a controlled laboratory experiment using sediment from Lakes Ann and Riley located in Chanhassen, MN, to 1) evaluate the response of the seed banks to different treatments and 2) compare the observed taxa sprouting from the seed banks to the taxa observed growing in the lakes. The treatments included a maximum germination treatment using a germination promoter to evaluate the full extent of the viable seed bank, a treatment representative of a lake with good water clarity, and a treatment representative of a lake with poor water clarity. The good and low clarity treatments were designed to evaluate the response of seeds to two different light levels that were observed in lakes with high turbidity (low-light intensity) and low turbidity (high light intensity). It was hypothesized that the maximum germination treatment would have the highest amount of germination, the high clarity treatment would have the second highest amount, and the low clarity treatment would have the lowest amount of germination due to the low-light quantity. The seed banks of both Lakes Riley and Ann were similar to the macrophyte community observed growing in the lake. In Lake Ann, 16 species were observed sprouting and every species observed in the experiment grew in the lake. In Lake Riley, 17 species were observed sprouting and all but two species were observed both in the lake and in the seed bank. The seed banks did not show any significant difference in response to the germination treatments. Chara, curlyleaf pondweed, and wild celery were the most frequent species observed. Under maximum germination conditions, Lake Riley had a viable vascular seed density of 2,916 ± 1,828 seeds/m2 and a viable chara spore density of 1,033 ± 698 spores/m2. Lake Ann had a viable vascular seed density of 1,100 ± 440 seeds/m2 and viable chara spore density of 13,833 ± 2,825 spores/m2. The study demonstrated that germinating propagules from a lake seed bank can be a valuable tool for managers to evaluate the viable macrophyte taxa present and better understand the potential for recruitment from the seed bank. Overall, to restore native macrophyte communities, it requires several multi-year management actions and will likely include multiple forms of propagule recruitment.