Effects of Climate Change on Riparian Vegetation Structure, Water Uptake, and Dependent Pollinators along Mainstem Rivers in the Colorado River Basin

Project ID: 310
Principal Investigator: Mark Nelson
Research Topic: Ecosystem Needs
Priority Area Assignments: 2010 (Climate Change and Variability Research), 2011 (Climate Change and Variability Research), 2012 (Climate Change and Variability Research)
Funded Fiscal Years: 2010, 2011 and 2012
Keywords: None

Research Question

Riparian habitats along regulated rivers are important providers of native insects to pollinate nearby irrigated orchards and crop fields. Most fruit, vegetable, seed crops, and crops that provide fiber and fuel, as well as some forage and hay crops (e.g., alfalfa and clover), are animal pollinated. Commercially managed bees are suffering serious declines due to introduced parasites and pathogens (National Academy of Sciences 2007), increasing the importance of native pollinators in agricultural production (Winfree et al. 2007). The populations of native pollinators relying on riparian habitats, in turn, are tightly coupled to the status of riparian plants and on the processes that ensure plant population persistence. Both of these factors are strongly linked to river hydrology.

Along river reaches where flows are strongly affected by Bureau of Reclamation (Reclamation) water management operations, the impacts from climate change on riparian habitat are expected to be felt through changes in operations as well as through independent changes in air and soil temperatures. Changes in water management operations are expected in response to changes in reservoir inflow timing and quantity, in evaporative losses, and in the timing and amount of downstream demand. Thus, it is important for water resource managers to understand:

* Whether potential effects from climate change on water management operations could exacerbate negative effects from climate change on riparian plants and habitats that support pollinators.

* How water management operations might be adjusted to optimize water delivery and potentially benefit riparian pollinators.

The literature review and biological research proposed here will help bridge these information gaps. Although not part of this proposal, it is expected that results from this work will be coupled to water operation models to assess environmental impacts of various management scenarios.

Need and Benefit

Reclamation has a need to understand how the environmental costs and benefits of its water management operations will change as local and regional environmental conditions change. It is clear that climate change will be affecting the supplies of, and demands for, Reclamation-managed water in the decades ahead. The exact nature of those changes, however, is uncertain. It is also clear that riparian habitats along both regulated and unregulated rivers are increasing in value as the total extent of such habitat is reduced through reductions in instream flows and land use changes. It is unlikely that riparian areas will decrease in value, and climate change, by reducing precipitation levels in some headwater areas, may accelerate any increase in their value.

Coupled with these environmental changes are changes in the animal populations that pollinate 66 percent of the world's crop species and contribute tens of billions of dollars per year to the United States' agricultural economy. The National Academy of Sciences (NAS) (NAS 2007) noted the vital importance of native (i.e., wild) pollinators to American agriculture, as well as to the natural habitats supporting them, including riparian areas.

The presence and abundance of wild pollinators provide insurance against the loss of managed pollinators (e.g., the European honey bee) that are declining as a result of introduced disease and parasites. For example, Kremen et al. (2002) showed that native pollinator communities from nearby natural habitats could provide full pollination service to a California crop (watermelon) with high pollination requirements. Studies in New Jersey and Pennsylvania have shown similarly high levels of importance for native pollinators in crop production (Winfree et al. 2007).

However, the NAS study found convincing evidence of local and regional declines in wild pollinators (both vertebrate and invertebrate) due to habitat degradation and loss and recommended that protection and maintenance of native pollinator populations become a national priority. The NAS also noted that changes in phenological synchrony and in distributions of pollinators and plants resulting from climate change could lead to a decline in interactions between flowers and pollinators, further jeopardizing native pollinator populations.

Thus, there is a need for Reclamation to understand how its water management operations may be affecting native riparian pollinator populations and how those effects may be modified as a result of operation changes undertaken in response to climate change. The proposed work will benefit Reclamation by providing information of use in the development of both current and future water management scenarios that include environmental benefits and costs.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Independent Peer Review

The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.

Floral ecology and insect visitation in riparian Tamarix sp. (saltcedar) (interim, PDF, 642KB)
By Doug Andersen
Publication completed on April 15, 2013

Climate change projections for semiarid and arid North America include reductions in stream discharge
that could adversely affect riparian plant species dependent on stream-derived ground water. In order to
better understand this potential impact, we used a space-for-time substitution to test the hypotheses
that increasing depth-to-groundwater (DGW) is inversely related to Tamarix sp. (saltcedar) flower
abundance (F) and nectar production per flower (N). We also assessed whether DGW affected

Vulnerability of riparian ecosystems to elevated CO2 and (final, PDF, 642KB)
By Doug Andersen
Publication completed on April 15, 2013

Riparian ecosystems, already greatly altered by water management, land development, and biological invasion, are
being further altered by increasing atmospheric CO2 concentrations ([CO2]) and climate change, particularly in arid
and semiarid (dryland) regions. In this literature review, we (1) summarize expected changes in [CO2], climate,
hydrology, and water management in dryland western North America, (2) consider likely effects of those changes on
riparian ecosystems, and (3) identify cri

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Effects of Climate Change on Riparian Vegetation Structure, Water Uptake, and Dependent Pollinators (final, PDF, 386KB)
By Mark Nelson
Publication completed on September 30, 2012

This bulletin summarizes the research results and potential application to Reclamation's mission.

Construction and Testing of a Soil Temperature Modification Unit for Climate Change Studies in Remote Areas (interim, PDF, 189KB)
By Mark Nelson
Report completed on April 15, 2013

Data from a pilot study, in which solar energy was used for subsurface heating, suggests that such an approach may be useful for modifying soil temperatures. Direct and indirect solar energy was harvested with a water heated collector and a photovoltaic powered pump. Soil temperature data were collected. Average soil temperature increased 1.15oC over ambient temperatures. The small inexpensive energy system performed as predicted over the approximate 4 month study and increased growing degree da

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Last Updated: 6/22/20