Ronald J. Hall

Experimental Acidification of a Stream in the Hubbard Brook Experimental Forest, New Hampshire

Incident precipitation in the northeastern United States averages about pH 4 as a result of increased pollution from sulfuric and nitric acids. To determine the effect of this increased acidity on the ecology of aquatic ecosystems, dilute concentrations of sulfuric acid were added to Norris Brook, a stream in the Hubbard Brook Experimental Forest, West Thornton, New Hampshire, USA. The stream was maintained at pH 4 from April to September 1977. With increased acidity stream water concentrations of Al, Ca, Mg, K, and probably Mn, Fe, and Cd were elevated; no change in dissolved organic carbon (DOC), Na, NO,, NH4, Ni, Pb, Cu, or Zn occurred at the lower pH. Emergence of adult mayflies (Ephemeroptera), some stoneflies (Plecoptera), and some true flies (Diptera) decreased at the lower pH. Larger numbers of immature aquatic inver- tebrates in the collector, scraper, and predator functional groups were found in drift samples from the experimental area during the 1st wk after acid addition. After the 1st wk of increased acidity total numbers of organisms drifting in the experimental area were similar to values obtained in the reference area. Emergence of adult collectors and invertebrate density in the benthos decreased in the treatment area. Periphyton biomass increased at the low pH, but hyphomycete fungal densities decreased. A basidiomycete fungus increased in the experimental area relative to the reference section. Brook trout showed no morphological signs of stress at the low pH. Stream acidification decreased species di- versity, increased representation of community dominants. and decreased the complexity of the food web.

The Role of Drift Dispersal in Production Ecology of a Stream Mayfly

The role of drift behavior in the production ecology of the mayfly Tricorythodes atratus McDunnough was investigated in a headwater reach of the Mississippi River in northern Minnesota, USA. Comparison of drift and bottom samples revealed that larger nymphs exhibited a greater pro- pensity to drift; in bottom samples, small immatures (1-2 mm) were predominant in a study riffle, whereas larger nymphs (>2 mm) were relatively more abundant in a downstream pool. Annual production was 8.56 gm 2. yr~-2 -I (dry mass) and the annual turnover ratio (annual production/annual mean biomass) was 26; the species was bivoltine. Errors in production rate estimation resulting from sampling a single habitat were substantial when differential size dispersal of nymphs occurred.

Effects of Experimental Acidification on Macroinvertebrate Drift Diversity in a Mountain Stream

A small stream (Norris Brook) within the Hubbard Brook Experimental Forest was acidified to determine what effect elevated H + stress may have on the ecology of a mountain stream. The experiment was designed to simulate a pH level (4.0) that can occur during initial snowmelt (acute period) and during longer term (chronic period) acidification. Daily macroinvertebrate drift samples were collected from treatment and reference areas of Norris Brook. Drift diversity at the generic level was calculated using Brillouin’s formula and partitioned hierarchically following macroinvertebrate classifications based on taxonomy (orders) and feeding strategies (functional groups or guilds).