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Simulation on Annual Change of Periphyton Biomass in the River
Abstract
In the Hinuma River, changes of periphyton biomass were observed weekly from September 1987 to March 1990 and compared with a model simulation to evaluate the dynamics of periphyton biomass.
A model was developed for simulating the periphyton biomass in a river system. The model consists of two sub-models : growth and scouring models. Parameters of the growth model were estimated based on the daily observation for a two-week period in each season. The change of the periphyton biomass was compared with that calculated through the model. Reasonably close agreement was found between the observed and calculated biomass ; however, a significant deviation was observed for the winter seasons when the biomass loss did not occur through scouring due to storm events. This deviation may be caused by significant detachment of the periphyton biomass and intensive grazing by benthic animals during the winter seasons.
The annual growth of periphyton biomass and the annual periphyton biomass scoured were found to be 110 g·m⁻² and 80 g·m⁻² as carbon, respectively. The periphyton communities may absorb dissolved nitrogen and phosphorus from river water for their growth. If this is case, in the Hinuma River, at 10-km downstream, 0.6% and 6.7% of the dissolved nitrogen and phosphorus in terms of the annual runoff loading may be utilized by the periphyton, respectively.
The landscape of a small pond in Fukuoka prefecture has been ruined by floating algae. Basic information, such as the type of algae, location of occurrence, and the amount of generated floating algae, was required to take action. In this study, we identified the floating algae by polarizing microscope observation and microbial community analysis. Additionally, we conducted aerial investigations using a multicopter equipped with a visual and near-infrared camera, and we quantified floating algae areas using images obtained from aerial observation. The results revealed that the floating algae were primarily made up of filamentous cyanobacteria from the family Pseudanabaenaceae. They mainly grow in the shallow area of the pond and peel off from the shallow bottom of the pond because of proliferation-related bubbles in summer. In addition, there was a relationship between the increase and decrease in algae carbon calculated using water temperature and solar radiation and the fluctuation in aerially observed algae area, suggesting that measures to limit solar radiation may be effective as a means of controlling algae proliferation.
Large quantities of attached algae grow in shallow urban rivers that receive nutrientenriched effluent from secondary sewage treatment plants. Deterioration of water quality caused by respiration and detachment of attached algae is observed in these rivers.
The kinetics of growth and detachment of attached algae in a circulation-type artificial river are studied in order to determine parameters involved in a water-quality simulation model of shallow and polluted rivers.
First-order rate constant of algal detachment was found to increase with aging of attached algal community. And on the basis of the fact that only this surface layer of attached algal community (about 0.2g chlorophyll-a/mm²) receives sufficient light for growth, a kinetic model for the growth and detachment of attached algae is defined.
Phosphate enrichment experiments were conducted year-round at the experimental troughs research apparatus (EXTRA) on the South Thompson River in British Columbia to determine the relationship between external concentration of orthophosphate and the growth rates of lotic periphytic diatom communities. Growth rate saturation always occurred at a phosphate concentration of approximately 0.3–0.6 μg P∙L ⁻¹ . The maximum growth rate (μ max-P ) with phosphorus enrichment varied seasonally with temperature. The relative specific growth rates (μ:μ max-P ) as a function of external phosphate were constant. Seasonal changes in solar insolation (PAR) had no effect on the autotrophic community growth rates in unamended river water. Temperature exerted the most dominant influence on phosphorus-replete growth rates.
1. Periphyton chlorophyll a and ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers.
2. Mean annual flows in the rivers ranged from 0.94 to 169 m ³ s ⁻¹ , mean dissolved reactive phophorus (DRP) from 1.3 to 68 μ g 1 ⁻¹ , periphytic chlorophyll a from 4.6 to 73 mg m ⁻² . and AFDW from 2.8 to 16 g m ⁻² .
3. For eight of the nine rivers NH 4 ‐N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated ( P <0.01) with flow, and for seven rivers conductivity was inversely correlated ( P <0.05) with flow.
4. There was a hyperbolic relationship between flows and biomass, with chlorophyll a >100 mg m ⁻² and AFDW >20 g m ⁻² occurring most frequently in flows of <20 m ³ s ⁻¹ .
5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer‐autumn and winter‐spring in the three rivers where floods were absent.
6. Chlorophyll a biomass was more resistant to flooding than AFDW. Only 5993 of the forty‐six recorded floods caused chlorophyll a scouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre‐flood biomass than the magnitude of the event.
7. Biomass maxima were significantly correlated ( P <0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers.
8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel‐bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel‐bed rivers should always be viewed within the context of the flow history of the site, and not just as a function of nutrient concentrations.
Model predictions of periphyton biomass, as a function of ambient SRP concentration, were compared against observed biomass accrual on natural and artificial substrates in the Spokane River, Washington. A range in biomass was predicted based on uncertainties due to temperature, velocity, accumulation period and an empirical growth constant. Only 8 of 47 observed biomass values exceed the lowest biomass predictions, which supports the contention that the model represents the maximum potential biomass. Using the SRP concentration that would produce a threshold nuisance biomass (150–200 mg ch α/m2), an approach is proposed for controlling the stream distance for which periphytic biomass exceeds the nuisance level. For the Spokane River, critical distance with biomass exceeding 200 mg chl α/m2 may exceed 10 km unless SRP is held below 10 μg/l.
It is difficult to clarify when and how physico-chemical parameters regulate growth of periphytic algae. Many parameters are potentially involved, and these are usually measured in the external water. Growth rates of periphytic algae can be estimated during the early growth phase of the biomass, assuming that colonization and losses are of minor importance. During the later stationary or secondary phases it is necessary to quantify losses. During the early growth phase good correlations can be obtained between external parameters and the rate of biomass changes. In this phase the periphytic community is thin, and the rate of exchange with the external water, in proportion to internal processes, is relatively more important than in later phases, when the community becomes thicker and biologically more complex. Many submerged macrophytes continuously produce new tissue and slough off old tissue. The age of the tissue can sometimes be measured quite accurately. The rate of change in density of epiphytic algae with increasing age of tissue, or the mean density for all tissue ages, can be very sensitive to changes in inorganic nutrient loading. Carbon-14 and O2 exchange methods should be applied to studies of periphytic processes, realizing that these processes occur within a boundary layer, and have great potential for analyzing effects of time and depth changes in chemical parameters.
In the eutrophication analysis of a lake, it is essential to make clear the origins, constituents and amounts of nutrients discharged into the lake and the behaviour of nutrients in the lake which will be uptaken into and released from by the growth and decomposition of phytoplankton and zooplankton. In the research reported, a mathematical model has been proposed to predict the changes of water quality in a lake undergoing eutrophication. The general patterns of seasonal variations on the water quality items, were successfully simulated by the model. Typical seasonal variation on inorganic nitrogen in the lake is well identified, and the daily input loads of nutrients and organic pollutants are well allocated by the developed model.
The growth rates of microorganisms were determined for a periphyton community grown on artificial substrata submerged in the midstream of the Tamagawa River. The growth rates were measured seasonally for bacteria, algae, the heterotrophic periphyton community and the whole periphyton community. The doubling times were as follows : bacteria, 3-10 hours; sessile algae, 12-28 hours; heterotrophic periphyton community, 15-104 hours; and periphyton community, 12-59 hours. The growth rates showed a good correlation with water temperature, and the Q10 values were as follows : bacteria, 1.9; sessile algae, 1.6; heterotrophic periphyton community, 2.5; and periphyton community, 2.2.
A simple and an expanded model of periphyton dynamics in lotic environments are described. The simple model includes one level variable, the biomass of the periphyton assemblage, and four rate variables: primary production, community respiration, and two export fractions. In the expanded model three level variables and eight rate variables are added to the simple model to introduce the effects of allochthonous organic matter and grazing activities by an aquatic snail. In general, computer output from the expanded model supports the hypothesis that the relatively low biomasses of periphyton observed in the small streams of western Oregon are the result of grazing activities by aquatic animals, high silt loads during the fall and winter months, and the effects of a dense canopy of terrestrial vegetation on light penetration. Furthermore, the model indicates that it is bioenergetically feasible for a periphyton biomass of about 10 g m^-^2 ash-free dry weight to support a consumer biomass of 150 g m^-^2 or more if the productive capacity of the system is sufficient. The simulation models provided an analytical way of synthesizing the results of a number of experiments with periphyton assemblages, identified weaknesses in the experimental data, and provided insights into the dynamics of periphyton assemblages that could not be obtained by intuition alone or by examining the results of individual experiments.
In Hinuma River, changes of periphyton biomass were observed weekly from September 1987 to March 1990 to evaluate the dynamics of the periphyton biomass in the river. Periphyton were sampled from artificial substrates which were 10cm×10cm unglazed clay tiles. The tiles were submerged in the river more than one month before sampling.
At the high periphyton biomass, the ratio of carbon per dry weight of periphyton was low because a significant amount of inorganic particles such as clay and silt was trapped in periphyton. However, the ratio of carbon : nitrogen : phosphorus remained constant regardless of the change of the biomass. From April to October the periphyton biomass was low due to losses by scouring due to frequent storm events. In November and December, the periphyton biomass became greatest because of steady low flow in the river. From January to March, the biomass did not increase significantly due to low temperature even though the rainfall was low.
The scouring was found to be a main factor in the dynamics of the periphyton biomass in the river. The amount of the periphyton biomass (as carbon) after scouring was proportional to the exponent of the maximum flow during the storm.
It is well known that the three nutrient elements of carbon (C), nitrogen (N) and phosphorus (P), are very important in the eutrophication in enclosed coastal seas. The major source of the C, N and P is the inflow from rivers rather than the release from sediment in the closed sea. In Japan, the environmental quality standards which indicate organic pollution in both river and sea are different from one another; in a river, it is based on BOD and in the sea, on alkaline CODMd. Therefore, these different standards lead to difficulties in obtaining consistent water quality management of the water system from rivers to enclosed coastal seas. Hinuma River observed runoff loading of alkaline CODMd, BOD, C, N and P by weekly observation in 1988 and 1989. When the flow increases, the order of increasing ratio is phosphorus, followed by carbon, and nitrogen. It was found that 88% of phosphorus runs off in the form of particulate phosphorus and 84% of nitrogen runs off in the form of dissolved nitrogen; and though nitrogen runs off in an almost constant concentration, most phosphorus runs off during the high flow stage. The behavior of the particulate phosphorus after flowing in to the enclosed coastal sea is an important factor in eutrophication.
Eight different mathematical formulations of the photosynthesis-light curve for phytoplankton (up to and including light saturation) were recast in terms of the same two parameters : the initial slope CY, and the assimilation number P_M^B. Each equation was tested for its ability to describe empirical data from natural populations of marine phytoplankton: the results of 188 light-saturation experiments at three coastal locations in Nova Scotia over a 2-year period. The most consistently useful mathematical representation of the data was found to be the hyperbolic tangent function.
Development of Nuisance Periphytic Algae in Laboratory Streams in Relation to Enrichment and Velocity, Periphyton of Freshwater Ecosystem
- R R Honer
- E B Welch
- R B Veenstra