Introduction-Aquatic macroinvertebrates are well known indicators of water quaility. Some families such as ephemeroptera, plecoptera and trichoptera are especially sensitive to pollutants and are commonly used as indicators of water quality. Changes in land use can have negative impacts on water quality and these changes can be recognized by changes of macroinvertebrate assemblages (if data is available over time). One time samples can so be used as a "red flag" when compared to assemblages of aquatic macroinvertebrates found in a comparable stream free from pollutants.

Abstract=One of the largest contributors to global environmental change is the alteration of the landscape due to anthropogenic changes. In this study, we investigated the relationship of canopy cover and macroinvertibrate diversity in two streams. We found a higher diversity and higher corresponding water quality index in the stream with reduced canopy cover. We attribute this to the presence of autochthonous primary production.

Hypothesis-It has been shown in previous studies located in the Southern Appalachian Mountains that streams in pristine areas with canopy cover can have a very diverse aquatic macroinvertebrate fauna. In this study our team investigated the aquatic macroinvertebrate diversity in a second order stream with heavy canopy cover and a stream with no canopy. Our group hypothesized that the stream with full canopy cover located in the premontane wet primary forest would have greater macroinvertebrate diversity than the stream flowing though the pasture devoid of canopy cover. Our group felt the stream flowing through the pasture would have less macroinvertebrate diversity due to higher temperatures, and the possible presence of higher nitrates, herbicides and pesticides.

Study Area-Two streams were selected for this study. Both streams are tributaries of the Rio Java located in Las Cruces, Costa Rica. One stream is located in a tropical moist premontane primary forest within park boundaries and has heavy canopy cover. The second stream is located in an agricultural area currently being used as a cattle pasture. There are a few scattered small trees adjacent to the stream in the pasture with complete ground cover consisting of tall grasses and herbaceous plants.

Procedure-Both the primary forest tributary and the agricultural area tributary were sampled using a kick-net of dimensions 40 cm X 75 cm. Three kick-net samples were taken from each stream. A 0.5 m by 2 m substrate area was disturbed for 3 minutes by vigorous kicking. The net was then removed from the water. Specimens were collected from the net by two individuals for twenty minutes. They were then field identified and placed in alcohol. Submerged rocks and leaf packs were also searched for specimens. This procedure was started downstream and repeated at three different points at approximately 3 m apart.

Temperature, pH, and dissolved oxygen levels were tested and recorded. A water quality index was assigned for each stream.

Results-A water quality index was calculated using a point system assigned to each order of macroinvertebrate found at each site. 3 point for sensitive orders, 2 points for falcultatrive (somewhat sensitive) and 1 point for each tolerant order.

Conclusion-The higher diversity in the stream with negligible canopy is probably due to the presence of autochthonous plant material in the form of algae. Algae were absent in the forest stream due to canopy cover that inhibited light penetration. The presence of algae accounts for the increase in the diversity of scrapers and grazers living in the agricultural stream. The increased number of herbivorous macroinvertebrates provides more prey for predacious macroinvertebrates such as dragonflies and damselfly nymphs. This would explain the faulty hypothesis. However, this study illustrates how stream fauna could be effected by global environmental change.