| Key Term |
Definition |
| Hydrology |
concerned with earth's water, especially its movement in relation to land. |
| Groundwater |
is held underground in the soil or in pores and crevices in rock. |
| Microclimate |
the climate experienced by organisms in a very small or restricted area |
| Aquifer |
body of permeable rock that can hold or transmit groundwater |
| Community |
group of associated species (of plants and/or animals) |
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Groundwater levels as well as local hydrologic features have a profound effect on the landscape we see in the Rio Grande valley. This is because annual precipitation is slightly more than 9 inches per year, very dry and intermittent . Water is very limiting for plant growth. One very easy thing is to interpret how hydrology affects our landscape, using plant life.
Our goal is to compare plant species composition between two sites. One is xeric, one is not xeric.
| Site |
Year left fallow |
Elevation |
Feet above river level Elevation 4998' |
| Stop 1 |
~1950 |
4992 |
4 |
| Stop 2 |
1946 |
5219 |
231 |
Stop 1 is an abandoned irrigation ditch (abandoned circa 1949-50) 4 feet above river level. Stay on the paved path. There are other public paths, but because of horse riding, these paths are often churned up and full of horse droppings.
Stop 2 is a pullout next to field, part of an abandoned airport (Area undisturbed since 1946) visible from the roadside. Elevation is 5129', 231 feet above the river level. It is further above above the water table for reasonable plant roots to access. A few plants like salt cedar, Tamarix spp. can have roots down as deep as 150 ft (45.72m) which is an exceptional depth. There are pockets of salt cedar throughout the valley.
Both sites are above the aquifer formed most recently (see below).
How far above the water table is the important point.
Stop1 gets surface runoff during rain storms and the water table is in the root zone of larger plants like trees. Stop 2 has only precipitation for water input, some of which runs off into arroyos or small swales. Because the water table is too far down it is not generally accessible by plants.
Background on the Albuquerque Basin and its aquifer:
The Rio Grande Rift Valley is home to the Albuquerque Basin, the Rio Grande's largest. And there is large aquifer here. Our understanding of the aquifer and total water in it has changed since studies began in 1992. Groundwater in our large aquifer has accumulated in three main phases.
Newest sediment (near the surface):
Since the last years of the Ice Ages the Rio Grande river valley has been getting more sediment than it can carry away, depositing all new sediment. This new layer as much 61 meters (200 ft) thick in some places. There is groundwater in this newest fill, forming a thin aquifer, close to the surface, the thickest section of the sediments is in the river valley around the river terraces.
Less recent sediment and rock (sandwiched between newest and oldest):
The aquifer formed by Upper Santa Fe group(rock formation) is smaller than originally thought, but has the best water quality of the three "layers" of the aquifer. It lives only in the Easternmost part of the Rio Grande basin.
Older sediment and rock (deepest):
The lower Santa Fe group (rock formation) has low quality (hard) water and has low yields of water.
Stop 1:
Take short stroll South, down the paved path. To the immediate west of the trail there is a strip of vegetation growing in what was once a ditch. The ditch runs parallel to the trail for about 100 yards. From your vantage point above try to see what large and small plants are there; look for density of plant life, size variations. That is the community of plants we have where there is abundant soil moisture. A lot of extra moisture runs downhill from where you stand into the ditch during rainfall. This is typical of soils in in the Rio Grande Valley. They dry out so much that intense rainfall is more likely to run off rather than soak in. Especially on slopes like you stand on now. And many tree species have roots that run deep enough to find groundwater in the ditch when there is no rain. So the effective microclimate for the plants in the ditch is different - much more available moisture. And during the rainy season the soil in the ditch becomes saturated and does not allow additional moisture to move down easily.
Stop 2:
Hop out of the car and look about 50 yards to the East. Before clearing of the land for the airport, this was mixed pinon-juniper (Evergreens) and grass lands. From your vantage point what large and small plants do you see there now? Do you see where the runoff goes here? It runs into swales, and also into the cement ditches all over town that drain the rain water runoff into the river. The volumes of water during the monsoon rains are truly huge, sometimes. You drove over the bridge of one those manmade arroyos to get here. It is due South of your position, in case you got lost and had to come here the hard way. The swales have usually got one or two very lonely trees growing in them. Do you see any lonesome trees way out there? So the microclimate for this community is very, very dry compared to the ditch.
Questions:
1. Stop 1 - Knowing about runoff why would you suspect that standing water frequently occurs in the ditch?
Answer is one of A or B:
A. Because the water table is very close to the surface and lots of runoff can move downhill, it builds up faster than it can percolate into the ground
B. The plants in the ditch are unable to soak up water fast enough to get rid of the water
2. Stop 2 - How does lots of runoff impact the plant community you see here?
Answer is one of A or B:,
A. The community here at Stop 2 is more lush and green and has many more kinds of plants.
B. The community here at Stop 2 is very open with mostly grasses, weedy shrubs, and few trees.
Thanks for checking out an interesting feature of the Rio Grande Valley.