Melton Hill Reservoir

Dissolved oxygen

Dissolved oxygen rated good at both monitoring locations. A small section along the reservoir bottom at the forebay had low dissolved oxygen concentrations in May, but not enough to reduce the rating.  Dissolved oxygen has rated good at the mid-reservoir location all years monitored and typically has rated good in the forebay unless there was an extended period with low flow. Low flow conditions can allow water to sit long enough that oxygen in the lower water column becomes depleted as it is used in the natural process of decomposition. This was the case in 2000, 2001, and 2008 when dissolved oxygen rated fair at the forebay location.

Chlorophyll

Chlorophyll rated fair at the forebay and good at the mid-reservoir monitoring location. Average annual chlorophyll concentrations have shown an overall trend of increasing at both locations since monitoring began in 1991. Chlorophyll rated good at both locations during the 1991 to 1996 time period. Since 1998, chlorophyll ratings have fluctuated between fair and poor at the forebay and good and fair at the mid-reservoir location. Reservoir flows have played a part in the year-to-year fluctuations as low-flow conditions tend to allow more time for algal populations to become established.

Fish

The fish community rated fair at all three monitoring locations. Historically, the fish community has rated good or fair at the forebay, fair at the mid-reservoir location, and fair at the inflow monitoring location with the exception of 1994 and 1998, when the fish community rated poor.

Bottom life

Bottom life rated fair at the forebay and mid-reservoir locations and poor at the inflow.  The forebay and inflow locations  received their  highest scores to date, but there was no appreciable change evident in these communities — as in previous years, most of the organisms collected were species able to tolerate poor conditions.  Historically, scores for bottom life have fluctuated within the “low fair” to poor range at the forebay and within the poor range at the inflow location.  Scores have improved, however, at the mid-reservoir location since 1994 with scores shifting from the low end of the fair range to the middle of the fair range and even rating good in 2006.  The improved ratings were primarily due to an increase in the number of organisms less tolerant of poor conditions.

Sediment

Sediment quality rated fair at the forebay because samples contained slightly more arsenic than would be expected to occur naturally.  The mid-reservoir location rated good because no PCBs or pesticides were detected, and no metals had elevated concentrations. Low levels of chlordane, a pesticide previously used to control termites and crop pests, were frequently detected in sediment samples from both sites in past years. Arsenic, PCBs, and copper also have exceeded suggested limits in past years.

See definitions of ecological health indicators and monitoring locations.