| ID |
1892 |
| Citation |
E.U. Schindler, D. Sebastian, L. Vidmanic, H. Andrusak, J. Stockner, M. Bassett, K.I. Ashley (2010) Arrow Lakes Reservoir Nutrient Restoration Program, Year 9 (2007), Ministry of Environment, Limno-Lab Ltd., Redfish Consulting Ltd., Eco-Logic Ltd., BC Institute of Technology. |
| Organization |
Fish and Wildlife Compensation Program - Columbia Basin |
| URL |
http://biodiversityatlas.org/reports/details.php?reportID=550&searchterms= |
| Abstract/Description or Keywords |
This report summarizes results from the ninth year (2007) of nutrient additions to Arrow Lakes Reservoir. These additions were conducted using an adaptive management approach in an effort to restore lake productivity lost as a result of nutrient uptake in upstream reservoirs. The objectives of this program were to (1) replace lost nutrients as a result of upstream impoundments and (2) to restore productivity in the Upper Arrow basin that would in turn rebuild kokanee (Oncorhynchus nerka) and other sport fish populations -rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) throughout the entire reservoir. Nutrients added were in the form of agricultural grade liquid fertilizer (10-34-0, ammonium polyphosphate (phosphorus, P) and 28-0-0, urea ammonium nitrate (nitrogen, N). During 1999 to 2003, the seasonally adjusted blend of fertilizer was modeled on the successful Kootenay Lake fertilization experiment. Results from 2003 onward suggested that a closer examination of monthly phytoplankton biomass, species composition and water chemistry parameters was required to adaptively manage the weekly nutrient loading schedule to optimize food web transfer of ‘new’ carbon. From 2004 to 2007 less phosphorus and more nitrogen was added than the 1999 to 2003 period to ensure an adequate nitrogen to phosphorus (N:P) ratio for optimal phytoplankton growth. In 2007, 46.8 tonnes of phosphorus and 267.5 tonnes of nitrogen were added to the reservoir. Adaptively managing the 2007 weekly nutrient loading rates resulted in sufficient nitrogen to phosphorus ratios suitable for phytoplankton growth. Monthly monitoring indicated Arrow Lakes Reservoir remained oligotrophic according to nutrient and chlorophyll a concentrations taken from 0-20 m integrated epilimnetic samples. Additional discrete-depth photic zone sampling at two stations in 2007 indicated that the reservoir was not nitrogen limited, an occurrence observed during 2001 to 2003. Overall phytoplankton abundance and biomass was slightly higher in 2007 compared to 2006 results. The temporal trend of phytoplankton was bacillariophytes and chryso/cryptophytes co-dominating in April to June with a shift to bacillariophytes being dominant in July and August with dinophytes, chlorophytes and cyanophytes contributing higher abundances in October and November. Zooplankton density and biomass, especially Daphnia was the lowest on record in the nine years of study. Lower Arrow had higher zooplankton biomass than Upper Arrow, a trend that followed previous years. In Upper Arrow only a few individuals of Daphnia were found during the entire sampling season. The decrease in Daphnia is potentially explained by a faster flushing rate of the reservoir than previous years and grazing by kokanee. The overall trend of mysid density and biomass in 2007 decreased compared to the 2006 results. Mysid density and biomass was higher in the fertilization period relative to the two year period prior to nutrient additions. The number of kokanee spawners in tributaries to Arrow Lakes Reservoir declined again in 2007 for the third consecutive year since their peak in 2004. Low returns in 2007 can be attributed to a combination of small spawner size, low fecundity and poor egg-to-fry surivival during the fall and winter of 2003. This emphasizes the importance of continuing to operate Hill Creek spawning channel to ensure that fry recruitment is not limiting to kokanee production in Arrow Reservoir. Mean size-at-maturity and fecundity of Hill Creek kokanee spawners decreased in 2007 compared to 2006 mainly due to the return of some 2+ spawners. The age and size of the kokanee have been variable during the nutrient addition period (1999 to 2007) with a temporary shift in age of maturity to age 2+ during 2000 to 2002 following exceptional growth in 1999. Since 2002, the majority of kokanee have been maturing at age 3+. Good growth starting in 2006 has again led to a shift to a mix of 2+ and 3+ spawners in 2007. A kokanee hydroacoustic survey estimate in the fall of 2007 indicated a lower pelagic kokanee density relative to 2006. The total of all age classes in the reservoir was only 5.5 million kokanee, compared to 9 million in 2006. Transect densities in 2007 ranged from 75-498 fishŠha-1 compared to 218-638 fishŠha-1 in 2006. The mean kokanee biomass in 2007 was 4.6Škg ha-1. During the pre- nutrient addition (‘control’) period (1993-1998), biomass was estimated at ~2.8 kg ha-1. The average kokanee biomass throughout the nutrient addition period (1999 to 2007) was 10.0 kg ha-1. An overall assessment of the nine years of nutrient additions to Arrow Lakes Reservoir indicates that the approach to restoring kokanee was successful. Kokanee biomass increased on average by three times indicating restoration was successful. The 2007 data indicated the transfer of nutrients from one trophic level to the next was not as effective as previous years of the program. Physical changes from increased discharge in 2007 could be attributable to this. The adaptive management approach of applying nutrients to Arrow Lakes Reservoir needs to be continuously applied to ensure favourable water quality and pelagic food resources for kokanee and higher trophic level insectivorous and piscivorous fish. |
| Information Type |
Report |
| Regional Watershed |
Arrow Lake |
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