Factors influencing biomass and nutrient content of the submersed macrophyte Egeria densa Planch. in a pampasic stream

Abstract

We identified factors influencing biomass and nutrient content in E. densa in an enriched pampean stream of Argentina. Physical (current velocity, temperature), chemical (pH, conductivity, dissolved oxygen, nutrient content in water and sediments), and biological variables (biomass and nutrient content of E. densa, biomass of periphyton and other macrophytes) were estimated at each sampling occasion, and mean monthly values estimated. Biomass and nutrient content in E. densa were correlated with these physical-chemical and biological variables. Biomass was positively correlated with ammonium in stream water (P<0.05) and sediment total nitrogen (P<0.01). Nitrogen showed a positive relationship with ammonium (P<0.01), and a negative one with nitrate and periphyton biomass (P<0.05). Phosphorus was positively correlated with soluble reactive phosphorus (P<0.01). The growth of other macrophyte species in the stream seemed to influence E. densa biomass, probably through competition for light. Current velocity was low and not significantly related with E. densa biomass; however, a flood at the beginning of the study washed the macrophyte stand downstream.

Photosynthetic rate of the aquatic macrophyte Egeria densa Planch. (Hydrocharitaceae) in two rivers from the Itanhaém River Basin in São Paulo State, Brazil

“…E. densa also grew in less favourable conditions, but with lower values of net photosynthesis. The survival ability of E. densa under unfavourable conditions was also demonstrated by Feijoó et al (1996) and this could explain the undesirable growth of E. densa in some aquatic ecosystems when the conditions are sub-optimal.…”

“…For the management of submerged species, it is important to know about the conditions that favour and/or limit their growth, and one way is to estimate the photosynthetic rate. The photosynthesis and respiration rates of submerged macrophytes are directly related to temperature and light (Menendez and Peñuelas, 1993;Menendez and Sanches, 1998), as well as to nutrient availability, including dissolved carbon and oxygen (Sand-Jensen, 1989;Madsen and Sand-Jensen, 1994;Feijoó et al, 1996;Madsen et al, 1998). These variables can affect the photosynthetic characteristics of the plant, both seasonally (e.g.…”

Capacidade de regeneração de Egeria densa nos reservatórios de Paulo Afonso, BA

“…Medidas em outros locais, geralmente em latitudes maiores, têm revelado biomassas apenas um pouco menores (Getsinger & Dillon, 1984;Feijoó et al, 1996;Wilcock et al, 1999). Atingido o limite de acumulação, a vegetação poderia restringir a produção de biomassa ao necessário para renovação das plantas mortas, das partes desprendidas ou predadas.…”

Metabolism in a macrophyte-rich stream exposed to flooding

“…Macrophytes play a key role in open streams (without riparian forest) by increasing physical heterogeneity, trapping fine sediments, and providing a habitat for epiphyton, invertebrates, and fish. The general pattern over the year shows a reduction in the amount of macrophytes during the fall-winter season and an increase in submerged plants towards spring, which reaches its peak in summer (Feijoó et al, 1996;Giorgi et al, 1998, Feijoó et al, 1999. In Pampean streams, the high submerged vegetation biomass (up to 500 g DW m -2 ) suggests that macrophytes and epiphytic algae contribute a substantial part of overall stream productivity.…”