Marshes and Meadows (contemplating water).
Before we start looking at some new aerial imagery, please allow me a brief detour to consider water on earth:
All water is on land, and most land is under water. Ok, some water is floating over land as water vapor, and some water is “in land” in naturally formed aquifers in the Earth’s upper crust. But my point still stands, almost all water on Earth is sitting or flowing above the Earth’s crust. For some reason, maybe because we are terrestrial creatures, we consider the ocean as “other” and different than the rest of Earth. There are some important differences between the water in the ocean, and that on the rest of Earth: the salinity (salt content), and the immense volume or amount of connected water molecules.
With the understanding that most water is flowing over land, we can look at landscapes and begin to see the water there. A lot of water will be surface water flowing as runoff, but a not insignificant amount of water is moving through living organisms. Children learn at a young age that plants draw water from the soil through their roots. My sixth graders learn that this process is powered by evaporation of water in the leaves, causing a chain of water molecules to then be drawn up though the vascular tissues originating in the roots and soil. When organisms consume other organisms, they are consuming proteins, carbohydrates, some other biomolecules, but also all the water contained.
Upper Truckee River - Snow & Ice - November 2020
When we begin to see water, we see that life on Earth is largely water, and that living organisms thrive or die by the availability of water and its ability to sustain other living creatures.
Another way to summarize this understanding: “The biology lives in the hydrology which flows through the geology.”
What does it mean for the hydrology to flow through the geology? Simply put: water will flow downhill until it can’t. Over time, the flowing of water can change the geology of an area through erosion, but in the meantime, liquid water is at the mercy of whichever way is down. If a raindrop lands on the peak of a mountain it will begin its journey downhill, following the contours of the earth (geology), and meeting up with other liquid water along the way. We call these areas of land with shared bodies of water watersheds, and this concept is very important to understand the ecology of a region. For example, in California, we have a mediterranean climate with a drought every summer. This past year it largely stopped raining at some point in early May, and didn’t begin again until November. Nearly half of every year in California there is insignificant amounts of precipitation, and organisms have adapted to that climate.
The Upper Truckee River Watershed. Map from the excellent modelmywatershed.org
Now, you might be asking yourself, how do organisms go half the year without water? The answer is, they don’t! Just because it hasn’t rained in six months doesn’t mean there isn’t any water nearby. If you’ve ever visited the Yuba River in the summer, you know water is flowing downhill where it will join the Feather River, enter the Sacramento River, merge with the San Joaquin in the Delta, and eventually exit into the Pacific Ocean. Where does all this water come from during the summer and fall? Largely from snowmelt in the Sierra Nevada. Throughout spring and summer, frozen water (snow) in the mountains is melting and beginning its journey downhill. It will collect in streams and rivers, which may lead to even bigger rivers, or in some instances lakes.
Which brings us to meadows and marshes (that was some detour!). Meadows and marshes are types of wetlands that are frequently flooded because of snowmelt or runoff. Marshes are located on the edges of large bodies of water and form a transition between the lake or bay and the upland habitat. In the San Francisco Bay, and other inlets along the California coast, marshes are flooded by tidal action, and because of the high salinity, plants that live in coastal salt marshes are adapted to both low oxygen soils and high salts.
There are also many marshes adjacent to Lake Tahoe. As rivers drain into the lake they spill over into the adjacent lands. The Upper Truckee River used to terminate in a massive marsh before it was channeled straight to the lake to make room for new housing developments. (Restoration of the Upper Truckee Marsh has begun and will restore a large area to natural marsh to filter out sediment and nutrients before draining into the groundwater or lake, you can read about that project here: https://www.capradio.org/articles/2020/07/17/how-a-marsh-restoration-could-help-preserve-lake-tahoes-famed-blue-hue/
Taylor Marsh - Vegetation Removal - November 2020
Meadows are another important type of wetland in the Sierra Nevada. As snow melts, much of it will runoff down the mountain, but depending on the soil type, water can also absorb and sink into the land. Meadows can slowly absorb water throughout spring as snow melts, and then provide a source of freshwater into the summer and fall. As we discussed earlier, access to freshwater is a necessity for life. When you hike in the sierras during the summer, you can tell where the meadows are functioning as water reserves because of the abundance of wildflowers and insects.
Tahoe Rim Trail - Tahoe National Forest - July 2016
Which (finally) brings us to the drone imagery of meadows and marshes in the Sierra Nevada. By collecting seasonal imagery of the Upper Truckee River, I’m starting to get a sense for what type of data is available from RGB (red, green, blue) imagery. As discussed in prior posts, vegetation coverage and height can be calculated, but also type as colors change throughout the season. Conifers stay green throughout winter, while deciduous trees and shrubs like aspen and willow yellow, then lose their foliage entirely.
The Upper Truckee in Three Seasons.
Can you find the two beaver dams built between July and September?
Stream width can be measured, and depth can be approximated by comparing imagery from season to season and using the digital terrain map from one season to calculate volume of water on a surface in a later season.
In a similar way, I’m wondering if snow volumes on a meadow can be calculated. The challenge with mapping snow is the visual uniformity which will be very challenging for software to stitch together in order to be useful for calculating height and therefore volume. Some ground-truthing (I will get to this post eventually) will need to be done to compare whatever data the software can calculate with actual measured snow-loads. For now, I have two orthomosaics showing these landscapes with minimal snow to compare to prior maps (Upper Truckee), and to have for reference for future maps (Taylor Marsh).
Upper Truckee - Gathering Snow - November 2020
