080121-08MN006-Sabina Hackett River Project Proposal ... - NIRB

Description of the Existing EnvironmentLake benthos samples were collected from 26 lakes in August, 2007. Benthos samples werecollected from the same depth zones and locations as the sediment samples (shallow depth (0 -5m), mid depth (5.1 – 10 m), and deep depth (> 10 m)). This sampling design allowedcharacterization of the potential natural variation in lake benthos with both bottom depth andgeographic location. Lakes sampled lay within a number of different watersheds and includedtwo reference lakes located ~ 10 km away from the location of potential mining activities.DensitiesLake benthos densities varied significantly by replicate, lake depth, and between lakes,regardless of lake basin. The highest benthos densities occurred in the Camp Basin lakes Joe,Kathy and Banana (densities between ~8,000 – 14,000 organisms/m 3 within a depth zone).Although the Camp Basin possessed the lakes with highest benthos densities, it also possessedthe only lake to have no benthos found in any of the three replicates taken from a given depthzone; Camp Lake, Deep Depth.Benthic organisms were generally most abundant at shallower depths, although this was notalways the case.Taxonomic compositionLake benthic communities were dominated by a diverse assortment of Dipterans, althoughPelecypoda and Ostracoda were also prevalent. Although Dipterans and Pelecypoda weregenerally ubiquitous in the study area and occurred in approximately equivalent relative densitiesin all depths and lakes, Ostracods tended to be prevalent in only a few lakes, and more so inshallow areas. In general, the higher density shallows also tended to be more diverse in benthoscommunity composition.Anne Lake was conspicuous in its high density of nematodes (particularly at depth), a taxonscarce in other lakes in the study area. High benthos densities in Joe Lake, shallow depth, andKathy Lake, mid depth, were largely a product of large numbers of dipterans.6.2.5.5 Stream Benthic InvertebratesStream benthos samples were collected from 15 stream locations in August, 2007. Streamssampled lay within the Camp, Boot and Cleaver Basins, in addition to two reference streams andtwo locations along each of the Mara and Hackett Rivers; one upstream and one downstream ofany inflows potentially subject to future mining influence.DensitiesStream benthos densities ranged from a high of ~ 2,700 organisms/m 2 in Degaulle and Dog Lakeoutflows, to lows of ~ 300 organisms/m 2 in Thigh and Reference Lake A outflows and the Marariver downstream sampling location (MR2). For the Hackett River, stream benthos densitieswere higher downstream compared to upstream, whereas this pattern was reversed in the MaraRiver.January 2008 Hackett River Project – Project Proposal Sabina Silver CorporationReport Version B.1 6–6 Rescan Environmental Services Ltd. (Proj. #833-2)