This is Part III of our Data User’s Guide. If you haven’t read Part I and Part II, you’d get a lot more out of this article if you did read them first.
How to investigate streams at a detailed level is the subject of this case study. In RI, the Water Quality Office published a shape file of WQ designations across the state, and included a code for Cold Water (blue), Warm Water (purple), and “unattributed” (black) habitat. The “unattributed”, as you’d expect, is typically the “in between” water where streams turn from cold to warm. See the image below, which illustrates the full width of RI.
The basic way development destroys trout habitat is through a combination of cutting down trees (which destroys shade, that keeps the water cool), and paving (which creates an imprevious surface that just sluffs-off water). Instead of water staying in the soil in cool shade and getting absorbed into the aquifer, the warm rainwater flows directly into the streams. Roads can increase erosion and siltation in the watershed. Silt reduces the good spawning areas which require “complex”, gravelly bottoms. Runoff also carries soil and chemicals from the surrounding areas (especially fertilizers) which can stimulate algae growth, and steals oxygen from the fish.
Brook trout are particularly susceptible to these kinds of issues, since they need cooler, more heavily oxygenated water. A study in the state of Maryland found no brook trout in any watershed with greater than 4% impervious surfaces.
In the photo above, you can see the Providence metro area, marked with an “A”, which is built on a series of extirpated basins (we’ve increase the transparency of the extirpated basins in this view, so you can see a little of the base aerial imagery).
While this area would have been at one time almost entirely cool water streams, note that virtually all of the streams are now warm water. The only exception is that cluster of streams to the NE. It turns out that these are running through a series of conservation areas: Lincoln Woods State Park, the Aldrich-Marshal Woods, and an area shown on the map as the “North Central Conservation Area.” The town of Lime Rock is part of this area, so without looking at a geologic map, I’m betting there’s some limestone at play here. Obviously, if you were living in Providence, and wanted a close-by WTS, this area would be one of the first you’d explore.
But to understand the dynamics in other parts of the state, let’s zoom in on basins B and C. Note that B is an “orange” basin (it’s not completely clear, because it borders some “yellow” ones). This is the second-worst quality habitat that might still hold some brooktrout. C is “yellow”, which is a step up. I would venture at least some of these stream hold bookies. The question is why? Look at the close- up below.
Note basin B (orange) has two major roads cutting through it E-W, and one going N-S. What you can’t see at this scale, but you can easily recognize if you zoom in, is that the there is a network of smaller “country” roads across the entire area. The pattern of development, just judging fromt he photos, is “upscale country homes”… fully detached homes of fairly subtantial size, surrounded by significant areas of undeveloped land. This style of “exurban” sprawl, low density as it is, degrades the fish habitat. Note that several of the streams have degraded to warm water. Still, it’s possible that several of the others might fish OK, and would probably hold rainbows and/or browns.
At first glance, basin C (yellow) looks pretty similar. But when you zoom in, you realize that the development near the streams is a golf course. There are no roads at all, except for the country club’s driveway. Of course, run-off from a golf course can be a problem, but perhaps it’s being controlled pretty well. When you look in detail, you see that there’s a buffer of trees around most of the streams
The result is that all of the streams are still cold water, and imo, are likely to hold brook trout. If anyone knows them, let me know.
Of course, if you only had the basin data, you wouldn’t know with this level of precision about what’s going on with the individual streams. You could certainly zoom in and inspect the level of development. Your goal would be to avoid areas with more intensive settlement, and try to focus in on the more pristine habitat. You won’t really know what’s going on until you show up. But isn’t that the fun part?
The good news is that you have a lot to choose from. In exploring an area like this, it’s a good idea to pick out three or four streams to check out. If you find that one is a disappointment, or turns out to be inaccessible, you can check out another stream segment.