Importance of Dissolved Organic Nutrients to Streams

When leaves fall into streams, soluble nutrients and labile carbon compounds are leached out. Leaf decomposition occurs in three phases: (1) leaching of soluble compounds; (2) microbial and fungal colonization and degradation; (3) physical abrasion and fragmentation by macroinvertebrate consumers (Abelho 2001). The majority of leaching occurs within 48 hours - 7 days of a leaf entering the stream and may account for 4 - 42% of mass loss. Dissolved organic matter (DOM) is often the single largest pool of organic carbon in streams (McDowell and Fisher 1976).

Algae and bacteria take up dissolved organic carbon (DOC) during primary production. Even though as much as 42% of DOC inputs in the fall are due to leaf litter leachate (McDowell and Fisher 1976), DOC concentrations in streams rarely change during litterfall (Allen 1995). This is because the highly labile compounds and simple sugars from leaf leachate are usually taken up within 48-72 hours (Lock and Hynes 1976). Dahm (1981) found that 97% of the DOC from 14C labeled was removed from the water column within 48 hours by microbial uptake and adsorption onto colloid particles.

Algal Ecology

Leaves from riparian different species of riparian vegetation have different chemical characteristics (see table) and therefore contribute nutrients to streams in different ratios. Different nutrient levels in streams may contribute to differential agal growth (primary production).

Native Species	Common Name	C:N ratio	% N	% P	Data Source
Populus deltoides	Plains Cottonwood	19.7	2.38	0.94	Ostrofsky 1998
Salix nigra	Black Willow	2.24	2.24	0.12	Ostrofsky 1998
Exotic Species
Elaeagnus angustifolia	Russian olive	28.1	1.8	NA	Royer et al. 1999; Simmons & Seastedt 1999
Tamarix spp.	Tamarisk / Saltcedar	53.9	1.35	0.07	El-Beheiry and El-Kady 1998;Kennedy 2002

 

How does algal biomass vary in leachate extracted from native and exotic leaves?

Our task: We would like to compare the growth rates/biomass accumulation of algae in leachate extracted from native and exotic leaf litter. We will conduct the experiment in recirculating chambers (or aquariums) in the lab (classroom) using pre-colonized tiles as algal seed.

Experimental Design: We have to decide how many replicates to run, how often to harvest the experiment / collect data, and whether we'd like to identify the algae that grows on the tiles and/or determine chlorophyll concentration in the algae.

Tile Substrate Preparation: Unglazed tiles will be submerged in the Poudre River near Watson Lake for 2 weeks prior to the experiment. Tiles will be scrubbed with a soft brush and rinsed to remove most of the periphyton immediately prior to placing them in the chambers.

Leaf Leachate Preparation: We have Russian olive, tamarisk, cottonwood, and/or willow leaves. We can choose to use all four leaves or increase replication with fewer leaf types. Leaf leachate will be produced by soaking ___ grams of ground leaves in ___liters of water for ___ hours (summary of methods used by other researchers in table below). Leachate will be filtered through a 0.45 µm filter and then immediately placed into the chambers with tiles.

Leaf Size	Leaf Powder	Distilled Water	Leaching Time / Temp	Experiment Length	Data Source
1 mm	15 grams	20 liters	3 hours	4 days	Lock and Hynes (1976)
4 cm	50 grams	1 liter	1 hour	100 days	Cleveland et al. in press

Results: We will determine the algal biomass by scrubbing the algae off of the tiles with a soft brush (toothbrush). The water from the aquarium will be filtered through a 0.45 µm filter and dried. Dry mass will be used to determine the growth rate. We will compare the different treatments with standard t-tests and analysis of variance (2-way ANOVA).

 

References

1. Abelho, M. 2001. From Litterfall to Breakdown in Streams: A Review. The Scientific World Journal 1: 656-680.
2. Allen, J. D. 1995. Stream Ecology: the structure and function of running waters. Kluwer Academic Publishers.
3. Dahm, C.N. 1981. Pathways and mechanisms for removal of DOC from leaf leachate in streams. Canadian Journal of Fisheries and Aquatic Sciences 38: 68-76.
   
4. El-Beheiry, M. A. H., and H. F. El-Kady. 1998. Nutritive value of two Tamarix species in Egypt. Journal of Arid Environments 38: 529-539.
   
5. Lock, M.A. and H.B.N. Hynes. 1976. The fate of 'dissolved' organic carbon derived from autum-shed maple leaves (Acer saccharum) in a temperate hard-water stream. Limnology and Oceanography 21: 436-43.
6. McDowell, W.H. and S.G. Fisher. 1976. Autumnal processing of dissolved organic matter in a small woodland stream ecosystem. Ecology 57: 561-69.
7. Ostrofsky, M. 1998. Relationship between chemical characteristics of autumn-shed leaves and aquatic processing rates. Journal of the North American Benthological Society 16: 750-759.
8. Royer, T. V., M. T. Monaghan, and G. W. Minshall. 1999. Processing of native and exotic leaf litter in two Idaho (U.S.A.) streams. Hydrobiologia 400: 123-128.
9. Simons, S. B., and T. R. Seastedt. 1999. Decomposition and nitrogen release from foliage of cottonwood (Populus deltoides) and Russian-olive (Elaeagnus angustifolia) in a riparian ecosystem. Southwestern Naturalist 44: 256-260.

This project material is based upon work supported by the National Science Foundation under Grant No. DGE0086443. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Principal Invesitigator for the Colorado Front Range GK12 is John Moore and Co-PI's are Dave Swift, Bill Hoyt, Carol Seemueller, and Ray Tschillard. For more information contact Kim Melville-Smith.

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