A. The first of your questions on water chemistry is tough to cover in the space we have here. Dave Allan, in his textbook Stream Ecology, takes 20 pages to describe what you've asked, but he and I use only 3 pages in our book Streams: Their ecology and life to cover the subject for a lay reader. However, even three pages are too long for this column, so I'm going to just hit some highlights here and urge you to look for more details in a suitable book.

Obviously, the mix of chemical found in rivers and streams is important in determining the productivity of that stream. Two things are of utmost importance: (1) the buffering capacity as determined by the amounts of carbonate, bi-carbonate, and free CO2, and (2) the amounts of dissolved phosphorus and nitrogen. The first of the above essentially determines the amounts of available carbon that is necessary for the production of all organic matter via photosynthesis, and these amounts are influenced by the pH of the stream water. The totality of these relationships is measured as the alkalinity of the water. Phosphorus and nitrogen, particularly the latter, are essentially fertilizers that influence the ability of algae and other plants to grow. Other trace elements are important, such as silica for diatoms, but nitrogen and phosphorus are vital.

The acid neutralizing capacity of a stream describes the ability of a particular stream to react to inputs of acidic inflows, such as acid rain. Streams with a high capacity to neutralize acidic inputs show little adverse biological reaction to them. Streams that cannot neutralize inputs react by mobilizing forms of various metals, many of which are toxic, to adversely impact the biota. There is still a lot to learn about these relationships.

The above are cursory responses to your first question, and I would be more than happy to furnish you references to publications that could give you more detail. Suffice it is to say, that the chemical factors present in a stream are not only important in their own right, but interact variously with the physical and biological constituents to produce what you find in a particular stream.

The second part of your question on macroinvertebrate indicator organisms is a bit easier to answer. Several indices have been developed, some simple, others more complex, to allow biologists to evaluate the water quality of a particular stream. I've used one of the simplest with high school students with no training in taxonomy and it has worked fine. Basically, the indices rely on the collection of macroinvertebrates, determining the family-level classification, and then performing some mathematical manipulations to come up with a water quality index value. This number is then compared with values indicating relative degrees of organic pollution.

Specifically, you ask what these organisms are. In very general terms, stoneflies are indicative of clean water conditions, as are most mayflies. Caddisflies range from clean-water taxa to those tolerant of some pollution. Midges also range from clean water to polluted conditions, while dragonflies and damselflies are fairly pollution tolerant. If you're looking for more specific information, here are some taxonomic family names that may help:

Clean water taxa: stoneflies (Chloroperlidae, Perlidae, Pteronarcyidae), mayflies (Ephemerellidae, Leptoplebiidae), caddisflies (Brachycentridae, Glossosomatidae, Lepidostomatidae).

Mid-tolerant taxa: mayflies (Baetidae, Heptageniidae), caddisflies (Hydropsychidae, Leptoceridae, Limnephilidae).

Pollution-tolerant taxa: mayfly (Siphlonuridae), damselflies and dragonflies (Coenagrionidae, Lestidae).

I can't put common names as used by anglers on these, but if you'd like to pursue this further, let me know and maybe we can do some clarification. I also don't know what resources you might have to identify these, but I'd be glad to help there, too.