Finally, a fundamental characteristic of these ephemeral stream ecosystems is that they are present for an unpredictable, short period of time, which places considerable time constraints on the survival of any organisms, invertebrate or vertebrate, that choose to inhabit these waters.
Blunt for their assistance in sampling under less-than-ideal circumstances in these ephemeral stream watersheds during the monsoon rains.
Aquatic communities of ephemeral stream ecosystems.
TABLE 1--Schedule of sample collection and day of succession (numbers 1-6) for ephemeral stream systems within the study area, 2006.
Because these ephemeral streams represent, for aquatic organisms, a small patch of habitat within an otherwise hostile environment, island biogeographic theories (MacArthur and Wilson, 1967) should apply.
We conducted a natural history study to survey the aquatic macroinvertebrates and vertebrates in several ephemeral streams in two regions in Arizona and New Mexico that flowed for short periods of time after monsoon thunderstorms (AWWQRP, 2006).
We could not test the last three days of succession statistically because the water in each of the Santa Cruz River watershed sites dried up by 96 h after flow began to recede, and we did not test ephemeral streams because there were only two sites per watershed.
This aspect of the study was constrained by the fact that less than a third of the streams studied were truly ephemeral streams, so the lower number of taxa is not surprising.
Controlling entrenchment of semiarid ephemeral streams is difficult because the extremely variable and dynamic conditions create stream behavior different from that where most hydrological principles and erosion control methods were developed (Bull 1997).
Soil bioengineering approaches (Gray and Sotir 1996) are also relatively material- and labor-intensive for such extensive application, and soil conditions of semiaridarid ephemeral streams where arroyo cutting is most prevalent may be too dry to support fast-growing vegetation.
Traditional Zuni erosion-control methods effectively modify channel morphology of entrenched headwater ephemeral streams after small flows and powerful floods in ways that increase the occurrence of overbank flows and the area of alluvial fans flooded by recurrence interval flows of less than or equal to five years.
Future studies should focus on identifying and sampling new habitats, especially the numerous wetland-like habitats that occur across the Colorado Plateau, such as hanging gardens and alcove pools, as well as ephemeral streams
, because these are poorly sampled and may be first affected by future changes in climate.