![]() ![]() This buildup is called a debris dam and it is another important feature of a healthy stream. You’ve probably seen instances where a large branch fell across a stream, resulting in a backup of other branches, twigs, and leaves. ![]() Woody debris can include anything from a fallen tree trunk to smaller branches. One way leaves can be caught within a stream is by getting snagged by another one of trees’ gifts to the streams: woody debris. ![]() Most leaves travel between 0-70 meters downstream before they are trapped (Abelho, 2001). The structure of a stream, from the way it curves to the distribution of riffles and pools, influences how many leaves it can capture and how long it can hold them for. ![]() In order for leaves to undergo any of those 3 processes that were just mentioned, they have to be held in the water for an extended period of time. (left) This leaf pack hides a plethora of tiny macroinvertebrates and microbes between the folded leaves (Photo Credit: Rebecca Lauver). Water trickles through the leaves and through a few open gaps to the sides and under the leaf build up. This debris dam is formed by larger branches intersecting across the stream. Shredders include some caddisflies, some stoneflies, amphipoda, some beetles, and a range of other macroinvertebrates. Pretty much they take big pieces of leaves and turn them into smaller ones that other organisms can eat as well. Shredders feed on leaves that fall into the stream, breaking apart this coarse particulate organic material (sometimes denoted as CPOM) into fine particulate organic matter (FPOM) that another feeding group, called collector/gatherers, can then feed on. There is also a feeding group of macroinvertebrates called shredders (in addition to scrapers, predators, and collector/gathers) that rip leaves into smaller pieces as well. You could imagine that during a flood, a leaf would get tossed around and caught on branches and rocks in the water, ripping it into smaller pieces. This can happen when fungus takes in parts of the leaves, by physical abrasion from the stream, or by being shredded by aquatic macroinvertebrates (Abelho, 2001). The final route a leaf can take is fragmentation. In a way, conditioning ‘cooks’ the leaves, making it an easier meal for other organisms, like aquatic macroinvertebrates, that may need some help with their digestion process. A conditioned leaf is easier for some other organisms to feed on. When a leaf is conditioned, fungi and bacteria in the water start to break down the leaf tissue and absorb nutrients for themselves. Pools of stiller water can also result in pile ups of leaves (Photo Credit: Rebecca Lauver).Īnother process that the leaves might undergo is called conditioning. You can see a variety of oak leaves, american beech leaves, and tulip poplar leaves and seeds on the streambed. The dissolved organic compounds provide important nutrition for the microbes and other organisms within the stream. Stroud Water Research Center has coined the combination of leached organic compounds and stream water as “watershed tea.” Just like when you stick a tea bag into a mug of water and see the tea disperse throughout the hot water, so do the nutrients from the leaves disperse throughout the stream. Leaching is when the soluble organic compounds in a leaf are pulled into the water. Once in the stream, there are 3 processes that leaves may undergo: leaching, conditioning, and fragmentation. Suddenly, the leaves find themselves in a wet environment filled with new microbes, aquatic insects, and a wild ride of riffles and runs. Whenever it is possible, it is always good to leave leaves on the ground where they are! If these leaves happen to be near a stream, there’s a good chance that some of them will make their way into the water. Leaf litter provides food and shelter for the organisms below and improves soil health. Once tree leaves fall to the ground, they turn into leaf litter. However, the second portion of the leaves’ lives have just begun- now is their turn to give back to the ecosystem that formed them! Once they are on the ground, it can be easy to forget about the ecological importance of these leaves. Newly fallen leaves rested on the tops of rocks, waiting for a gust of wind or higher waters to pull them into the stream (Photo Credit: Rebecca Lauver).Īfter a gorgeous season of fall foliage, the leaves of our deciduous trees turned brown and have fallen. There were still some green leaves hanging onto the trees when this photo was taken in Lancaster County, PA in late October. ![]()
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