Thursday 2 july 2015
17:57 - 18:00h at Central America (level 0)
Themes: (T) Water resources and hydro informatics (WRHI), (ST) Catchment hydrology
Parallel session: Poster pitches: 13H. WRHI - Catchment
A 19-month investigation was conducted into the water budget of Round Lake, a permanently stratified hardwater meromictic lake in Green Lakes State Park in central New York. Round Lake is a small headwater lake with no permanent surface inlet and one stream outlet that is located in a catchment of 0.84km2. The lake surface area is 0.13km2 and the volume is 4.65×106m3. The water budget was formulated on the basis of automated precipitation gauge measurements, bulk evaporation estimates from high resolution meteorological data, and discrete measurements of stream discharge and lake levels during ~80 site visits of over a 19 month period. Because of the simple geometry of the small steep-sided headwater basin, the lake water budget could be accurately assessed with this sampling approach and temporal trends resolved. Subsurface groundwater input is the most inportant single term in the water budget, accounting for ~3.5m/y of equivalent lake level rise. Spring runoff from snowmelt is the second most important term accounting for ~2.5m/y of equivalent lake level rise. Precipation falling directly on the lake surface accounts for ~1m/y. Most of this inflow passes from the lake through the outlet stream (~6.5m/y) with a small amount lost by surface evaporation (~0.5m/y). The high throughput of water gives an average residence of ~5y for the whole lake volume, or ~3y for the upper mixolimnion alone. More detailed examination of the groundwater inflow reveals a pronounced seasonal variation and a close association with rainfall events. The lake level changes in nearly discretized steps and behaves as if it receives groundwater from at least three subsurface reservoirs that overflow in sequence according to the local rainfall intensity. The nature of the water budget is important because the surface groundwater inflow at 20m depth maintains permanent stratification of the meromictic lake and contributes to maintain the special ecology of the calcifying cyanobacterial monoculture in the mixolimnion. Round Lake is potentially important as an untapped palaeolimnological archive of regional Holocene climate conditions.