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3.1.1 Periphyton Cover and Biomass


Goal: A. Maintain and improve water quality and supply to sustainably meet the needs of natural and human communities

Objective: 1. Maintain water quality for healthy aquatic systems

WAF Attribute: Biotic Condition

What is it?

Benthic algae are photosynthetic plants which are anchored to benthic sediment, rock, and each other on the stream bottoms or edges of aquatic systems. Together with submerged vascular plants, benthic algae are referred to as periphyton and are indicators of pollution and water quality (Shilling, 2007). Benthic algal cover is a food source for invertebrates which graze on the plant material and in turn the invertebrates are food sources for fish (Finlay et al., 2002) in the rivers, streams, and lakes. Periphyton is a relatively under-studied biological indicator of ecological condition, but it has an ecological connection to temperatures, nutrients, and benthic macroinvertebrates in determining the health of an aquatic system.

Why is it Important?

“Excessive algae growth” is a water quality concern and pollution indicator in the managed waterways of California and in the Sierra Nevada (Fetscher et al., 2009). It is defined as an amount of algae growth greater than a normal system’s output (Shilling et al., 2007). Algae can deplete aquatic systems of nutrients and algal communities can vary compositionally by the nutrients available (Marinelarena and Di Giorgi, 2001). High productivity of algae causes negative downstream effects to benthic DO levels (Lavoie et al., 2003), fixed carbon production, nutrient cycling, pH, food web structures, and health of fish (Shilling et al., 2007). Methylated mercury can be passed up the food chain to pose health risks to wildlife and humans, and bromine-reacted dissolved organic carbon (DOC) compounds (from algal decomposition) in drinking water are human health hazards (Shilling et al., 2007). Watershed questions can be answered by determining algal density and community structures by assessing the locations and severities of nutrients concentrations, of high temperatures which would naturally would be colder, of invasive species, of natural succession through seasonal changes (e.g., flow and temperature), and of land disturbances (e.g., water diversion, fire, or development activities; Shilling et al., 2007).

What is the target or desired condition?

Periphyton is naturally present in aquatic systems at all times of the year. It does create its own food source during colder temperatures and is distinguishable as a thin, colorless layer on rocks and benthic substrates. The metrics for periphyton used here were percent cover of benthos, dry weight, and ash-free dry weight (weight of organic material). Chlorophyll is sometimes used as a metric for amount of periphyton, but was not available here. For biomass weight measurements, a) the target ash free dry weight scores ranged linearly from the values of 10g/m 2 = score of 100 to 100 g/m2 = score of 0, and b) the dry weight scores ranged from the values of 20g/m2 = 100 to 200g/m2 = 0. A target of 0 g/m2 or zero percent cover is not ideal for most aquatic ecosystems, except for very cold and light limited conditions. Metric ranges for this analysis were determined by the UC Davis team from a preliminary pilot study conducted in 2001 & 2002 by Fraser Shilling (Shilling, 2007). For the percent cover metric, 100% cover = score of 0 and 35% = score of 100. The value 35% was chosen as the baseline value because it was the lowest summer maximum percent cover value of any subwatershed in the studied region of the Feather River Watershed and was assumed to represent natural conditions. A linear 1:1 function was used to calculate score, using values for percent algal cover and/or biomass of grams per meter squared. Again, since periphyton is under-studied, there are not published values for the Sierra Nevada, Northern California, or the state of California to use in setting standard maximum and minimum values for periphyton in health aquatic ecosystems. Publications for the region of Lake Tahoe are comparative studies in this discipline, but do not give guideline values.

What can influence or stress condition?

Algae can be nutrient-limited (Cascallar et al. 2003; Mc Cormick and Stevenson, 1998; Perrin and Richardson, 1997) by nitrogen and phosphorus concentrations, light-limited (Kiffney and Bull, 2000; Quinn et al., 1997a, b), and water temperature limited (Francoeur et al., 1999; Morin et al., 1999; Robinson and Minshall, 1998; Weckstroem and Korhola, 2001). Nitrogen and phosphorus, as nutrients, are readily absorbed by aquatic plants especially at levels greater than the naturally occurring low concentrations in aquatic systems. Nutrients and increased temperatures together will increase periphyton growth rates. Additionally, the riparian corridor on either side of an aquatic system shades and provide an external cooling system for the water. These same concerns of higher temperatures and/or lack of riparian cover and/or nutrient additions to an aquatic system can be due to land use practices or disturbances (Bojsen and Jacobsen, 2003; Cascallar et al., 2003; Chessman et al., 1999; Delong and Brusven, 1998; Giorgi and Malacalza, 2002; Harding et al., 1999; Siva and John, 2002; Winter and Duthie, 1998). Disturbances to the surrounding hillsides can remove riparian trees, remove root systems that hold soils, and add nutrient run-off into the rivers. Finally, seasonal changes in an aquatic system influence channel geomorphology and atmospheric climate and directly affects flows, substrate types, and temperatures. Lastly, a majority of California waterways are controlled by water management systems of dam, diversions, and canals which provide additional pressure on natural regulation of periphyton growth compared to historical conditions.

What did we find out/How are we doing?

The periphyton scores ranged from 5 (Deer Creek) to 100 (North Fork Feather and East Branch North Fork Feather, Figure 1 and Table 1) for all subwatersheds evaluated. The subwatershed with the lowest score was Deer Creek, which also had the richest data-set in terms of spatial distribution and years sampled. Subwatersheds with the lowest scores are assumed to be under greater stress in the watershed. The highest scores given to the East Branch North Fork Feather and the North Fork Feather were based on one year’s data from samples taken over a wide area. Currently, the Feather River and Yuba River are the only regions with percent cover estimates. Deer Creek and the Yuba River are the only regions with biomass measurements.

Table 1: Report Card scores for periphyton for subwatersheds

Goal Measurable Objective Subwatershed Score
A. Maintain and improve water quality and supply to sustainably meet the needs of natural and human communities 1) Maintain water quality for healthy aquatic systems — periphyton NFF 100
MFF 87
LF n/a
NY 73
MY 27
SY 29
DC 5
LY n/a
UB n/a
LB n/a

Figure 1: Periphyton scores distributed across subwatersheds

Temporal and spatial resolution

The spatial distribution of periphyton data was inconsistent across all subwatersheds. The time scale varied from 2001- 2009 for sampling conducted. A majority of sites in the Deer Creek and Feather subwatersheds were sampled in 2004. The greatest amount of data on a single time-frame were available for Deer Creek with 4 years of consistent sampling conducted, but otherwise there were few sites with replicated years of sampled data at the same site locations. The lowest temporal resolution collected data were collected in the single years 2001-02 and in 2004 at single site locations. The highest resolution of spatial data was found in the Feather subwatershed where 19 locations were sampled in the North Fork Feather, although it was all taken in one year. The overall spatial coverage of the subwatersheds was not very comprehensive for this analysis with data not available in the three lower subwatersheds and was not widely distributed within individual subwatersheds.

How sure are we about our findings? (Things to keep in mind)

The confidence in the overall finding of the reported values is assessed as a combination of variation in scores and how well the indicator reflects the environmental condition. An overall confidence is rated low for periphyton scores due to an overall relatively small geographic range of sampling, high variability in temporal collection, and lack of repetition of sampling. Therefore, the low overall confidence is given to all of the subwatershed scores with the recommendation that more data be collected in the future with similar protocols. There are two sets of guidance for measuring periphyton in California’s watersheds, which are complementary because they address different ways of measuring periphyton: The California Watershed Assessment Manual (CWAM), Volume II (Shilling et al., 2007, and the State Water Resources Control Board (SWRCB) Surface Water Ambient Monitoring Program (SWAMP) periphyton protocol (Fetscher et al., 2009). Nutrients and water temperature are complimentary indicators to periphyton and may be sampled at the same time. Benthic invertebrates can also be reported in conjunction with the periphyton assessments in the determination of potential pollution/perturbation.

Sampling intensity has been low in the subwatersheds, especially in the lower watersheds, where there were no accessible data. Data were collected at different temporal scales for the years ranging from 2001-02 and 2004-09, which led to inconsistencies in comparisons of all sites sampled. Also, periodic sampling (monthly) may not have captured the peak algae amounts which was the focus of the analysis, the highest sample value for each sampled year. There were metric inconsistencies where almost all watersheds did not have multiple metrics collected to average but within a metric there was consistency in collection methods. No trends or complex statistical analysis could be run due to the inconstancies in data availability. Overall a more robust set of data would be needed to conduct trend analysis for periphyton biomass or percent cover for the Feather River Watershed.

Technical Information

Data sources and transformations

Data was acquired for ash free dry weight, dry weight, and percent cover. In the Feather River Watershed, the subwatersheds with periphyton data were the North Fork Feather, Middle Fork Feather, East Branch North Fork Feather, North Yuba, South Yuba, Middle Yuba, and Deer Creek. Data were not available for the Lower Yuba, Lower Feather, Upper Bear, and Lower Bear. The Deer Creek data were collected from 2004 to 2008 (AFDW) at eight locations and was collected in 2001-02 dry weight at one location. The Yuba River data was collected from the years of 2006 and 2008-09, for the percent cover measurements at 14 locations; it was collected at three locations in 2001-02, of which one maximum value was evaluated for each subwatershed for dry weight. The Feather River subwatershed data in 2004 covered three separate types of algae with percent floating mats, percent macrophyte beds, and percent filamentous algae reported individually. The sum of these three percentages were used to get an overall, comprehensive percent cover of periphyton for each site location. The only excluded type of data reported was the percent emergent plants. Also the values were give in mostly whole numbers but for values close to zero, they were recorded as a <5% value. For these values less than five, they were converted to 5%. These "less than" numbers could not be assigned exact values, and for these purposes they were considered to weighted closer to five than to zero due to the idea that periphyton were present versus absent. For ash free dry weight, the highest values for each site were used for each sampled year to get an overall site peak value for the watershed. For dry weight, maximum values for the subwatersheds as the peak values at each site since only one year’s worth of data was available. There was not a most representative metric unit available for all sites and subwatershed score analysis was conducted on the averages of multiple metrics if available. All values were reported as raw values and no conversions were used to extrapolate the values into a different metric type (e.g., from percent cover to biomass).

Table 2: Average values for each metric and subwatershed with available data

Subwatershed Metric Values Percent Cover (%) Ash Free Dry
Weight (g/m2)
Dry Weight (g/m2)
East Branch North Fork Feather 35.0 n/a n/a
Middle Fork Feather 43.3 n/a n/a
Middle Yuba 91.1 n/a 27.7
North Fork Feather 25.9 n/a n/a
North Yuba 13.7 n/a 17.2
South Yuba 62.2 n/a 167.2
Deer Creek n/a 454.3 81.6

Table 3: Basic statistics for ash free dry weights, dry weights (grams per meter squared) and percent cover of periphyton across all sites. 95% C.I. refers to 95% confidence intervals.

Ash Free Dry Weight (g/m2)

Subwatershed Number of
algal cover
minimum maximum mean upper
95% C.I.
95% C.I.
Deer Creek 27 22.4 2664.8 454.3 735.1 173.4

Dry Weight ((g/m2)

Subwatershed Number of algal cover samples/year Values
North Yuba 1 17.2
South Yuba 1 167.2
Middle Yuba 1 27.7
Deer Creek 1 81.6

Percent Cover (%)

Subwatershed Number of
algal cover
minimum maximum mean upper
95% C.I.
95% C.I.
East Branch North Fork Feather 5 10 100 35 68.7 1.3
Middle Fork Feather 6 10 65 43.3 59.1 27.6
Middle Yuba 1 91.1 91.1 91.1 91.1 91.1
North Fork Feather 19 0 90 25.9 36.3 15.5
North Yuba 6 5 35 13.7 23.1 4.2
South Yuba 9 6 100 62.2 85.1 39.3

Condition Analyses:

Each metric was scored under a set range with the final score being extrapolated by the averaging of the multiple metrics, if available. The condition value was determined by averaging the raw values ( Table 2). Values for each metric, if more than one metric was available, were averaged to get the final subwatershed score (Table 1, Figure 1). For percent cover, each subwatershed’s set of data was plotted to give maximum algal coverage curves. The lowest maximum percent cover value (35%) was set as the lowest threshold and assigned the value of 100. A score of zero was given to 100% cover. Intermediate percent cover values were given correspondingly intermediate scores using a 1:1 linear function. For ash free dry weight, 10 g/m2 was given a score of 100 and 100 g/m2 was given a score of 0. For dry weight, 20 g/m2 was given a score of 100 and 200 g/m2 was given a score of 0. For both dry weight and ash free dry weight, the scores assigned were proportional to the parameter value’s distance from these targets.

Table 4: Separate scores for each metric used in the final condition analysis

Subwatershed Score
per Metric
Percent Cover Ash Free
Dry Weight
Dry Weight
East Branch North Fork Feather 100 n/a n/a
Middle Fork Feather 87.2 n/a n/a
Middle Yuba 13.7 n/a 40.2
North Fork Feather 100 n/a n/a
North Yuba 100 n/a 46
South Yuba 58.3 n/a 0
Deer Creek n/a 0 10.2

Trends Analyses

There was no consistently sampled location across years in any subwatershed, therefore no trends analysis was conducted.


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