Angela Dombrowski Algal Growth and Environmental Effects 19 April 2006 The Effects Of Nutrients Light and Insect Herbivory on Algal Biomass Angela Dombrowski Abstract Algae are an important source of primary productivity in stream ecosystems but the effect of nutrients on their growth in relation to light limitation and herbivory is not well known in lotic systems To better understand these two effects and the links between them I examined the response of algal growth to light availability nutrient availability and herbivory by the use of nutrient diffusing substrates nitrogen phosphorus and nitrogen phosphorus within the South Fork Eel River Mendocino Co CA The study was conducted within nine streams with varying degrees of canopy cover Of these nine streams four were chosen to examine the effect of herbivorous insects on increased algal growth Nutrient diffusing substrates were used to assess the effects of nutrients on algal biomass To see if herbivores respond to the expected increase in algal biomass by increased consumption and presence treatments allowing for herbivore inclusion were added Chlorophyll productivity and ash free dry mass AFDM biomass data were analyzed via multiple regression I concluded that nutrients when alone and not in conjunction with one another showed to have either an increased N or decreased P effect on algal productivity and biomass In a Two Way ANOVA herbivores were not shown to reduce organic biomass in streams nor did the data show them to have a significant preference towards nitrogen treatments This could mean that either algal abundance does not play a role in grazer nutritional preferences or that grazing of algae on nutrient treated substrates allowed other algae not preferred by grazers to colonize nutrient treated substrates p 1 Angela Dombrowski Algae and Environmental Effects 19 April 2006 Introduction There are many factors that affect trophic systems in streams and much has been studied regarding the variability of community structures in combination with differing environmental aspects Because algae are important in both primary productivity and nutrient cycling within aquatic ecosystems it is important to understand how the effects of nutrient limitation light and herbivory on algal growth and how these factors vary within streams Although much has been studied regarding algal reactions to environmental manipulation in marine and lentic lakes ponds ecosystems less attention has been paid to effects of nutrients light and herbivory in lotic ecosystems streams Nutrient and light availability in stream systems has an affect on various stream populations and processes such as algal growth invertebrates and leaf litter decomposition Elwood et al 1981 Peterson et al 1985 Hill and Knight 1988 It has been suggested that ratios of light to nutrient availability as well as the total availability of nutrients within the water column may have an effect on decomposition and invertebrate growth Elser et al 2000 Sterner and Elser 1997 Phosphorus nitrogen and a phosphorus nitrogen combination have been shown to limit algal growth in streams Elwood et al 1981 Fairchild et al 1985 Grimm and Fisher 1986 Tate 1990 Previous studies have shown that as light availability increases so does algal biomass Rier and Stevenson 2002 Hill and Knight 1988 Presumably as stream size increases canopy cover will decrease and hence microbial biomass will increase Hamilton et al 2001 In addition in situ shading experiments affecting light availability have shown to decrease chlorophyll concentrations of algae Hill and Knight 1988 Findlay and Howe 1993 It has also been shown that as stream size increase to 10 km2 algal production becomes increasingly important to all consumer groups excluding shredders In the case of streams smaller than 10 km2 consumer groups follow the River Continuum Concept of community consumption patterns Vannote et al 1980 Finlay 2001 It is suggested that this is due to a decrease in probably due to a decrease in terrestrial allochthonous inputs in relation to stream width and increasing algal production due to light availability Vannote et al 1980 The importance of algae for herbivorous invertebrates has been documented Hill et al 1995 Hill and Knight 1998 Lawrence and Gresens 2004 and various studies have examined p 2 Angela Dombrowski Algae and Environmental Effects 19 April 2006 the effects of nutrients in combination with herbivory Hill and Knight 1988 Finlay 2001 Rier and Stevenson 2002 Urabe et al 2002 This study examines how nutrient limitations and light availability affect algal growth in streams and how this growth is affected by herbivores This investigation is in essence an extension of previous research performed in the UC Angelo Reserve by Walter Hill and Allen Knight in 1988 The Hill Knight studies were conducted in two second order streams and consisted of two parts The first and most relevant to my study found that algal biomass and herbivorous insects were greater on substrates with increased nutrient availability in the unshaded stream Because increased algal biomass was found to be significantly greater in the shaded stream when light could penetrate the canopy it is suggested that light is a primary limiting factor in algal growth The second study found that caddisfly larvae Neophylax biomass was inversely proportional to the reduction of algal biomass and mayfly nymphs Ameletus were shown to be selective grazers In order to more fully understand how nutrient and light limitation affects algal growth within the stream drainage area of the South Fork Eel River I investigated how environmental differences and nutrient manipulations affect algal biomass within 9 streams and whether the number of herbivores on nutrient rich substrates is significantly different from control substrates The experiment concerning herbivores was conducted within 4 of the proposed 9 streams This makes the study an expanded in situ analysis of the Hill and Knight studies within the South Fork Eel watershed area allowing characterization of the environmental inputs that affect primary and secondary production The hypotheses are that there will be an overall increase in algal growth on pots that are equipped with augmented nutrient and increased light availability a greater presence of herbivores on pots that allow herbivore access as well as a decrease of algal biomass on herbivore inclusion pots Results complementing these hypotheses will suggest
View Full Document
Unlocking...