Impact of riparian trees shade on aquatic plant abundance in conservation islands

Abstract

Temperature, acidity, light conditions, total dissolved salts, conductivity, dissolved oxygen, submerged macrophytes and shade and sun path directions were measured at 23 sites along the River Nile banks with Acacia nilotica growing at water's edge around the First Cataract Conservation Islands. Ceratophyllum demersum and Potamogeton crispus were common in the shaded and unshaded zones, Myriophyllum spicatum and Vallisneria spiralis were found only in the unshaded zone and Azolla filiculoides only in the shaded zone. Banks of the sites surveyed were oriented to five directions (NW, SE, NE, SW, N). There is a significant difference in both the type and density of submerged plants growing under the shade of riparian trees (Acacia nilotica) as compared to unshaded areas. Water column irradiance is the most influential variable dictating the distribution of submerged plants. The area of the shade provided by riparian trees was affected by environmental and/or plant variables. Environmental variables comprised the daily course of the exposition to sun; and plant variables included the area of the tree crown, the height of the tree and geographical position of the tree in relation to sun exposition. Trees on the west bank of the islands at the SW-NE direction have the highest shading effect. The management of tree vegetation might control incoming solar radiation affecting submerged macrophytes.

The effect of ice phenology exerted on submerged macrophytes through physicochemical parameters and the phytoplankton abundance

“…competition on nutrients end allelopathic effects (Scheffer et al, 1993;Nakai et al, 1999;Pełechata et al, 2015). According to other studies (Ali et al, 1995(Ali et al, , 2011Ejankowski and Solis, 2015), we speculate that the light climate in this lake was still favourable for the SAV and much above the species tolerance level, independently on the type of winter.…”

“…The stronger effect on Myriophyllum spicatum L. and Stratiotes aloides L. than on Ceratophyllum demersum L. can be explained by their lower tolerance to water turbidity (Haslam, 1997;Szoszkiewicz et al, 2010). The shade tolerance of C. demersum seems to be the main factor responsible for the relatively high abundance and common occurrence of this species in many turbid water bodies (Ali et al, 1995(Ali et al, , 2011. Deteriorated water quality had a relatively small effect on the abundance of the hornwort that can potentially determine its strong competition ability in the lake ecosystems.…”

The Effect of Riparian Forest Shade on the Structural Characteristics of Macrophytes in a Mid-Forest Lake

“…Differences created by littoral geomorphology, water level fluctuation, variable light, and anthropogenic influences create a wide range of habitats for emergent and submerged water plants, as well as for floating-leaved plants (Feldmann and Nöges, 2007;Sender, 2010). Research suggests that greatly limits primary production in lakes thus it is speculated that managing for light could aid in the technical fight against overgrowing (Dawson, 1981;Spence, 1981;Ali et al, 2011).…”

Response of Hornwort (Ceratophyllum Demersum L.) to Water Level Drawdown in a Turbid Water Reservoir

“…The effect of annual water level regime on the submerged macrophyte was observed despite the light conditions -in the late summer they were generally worse than during the preceding period. The shade tolerance of C. demersum seems to be the major factor responsible for the species relatively high abundance and common occurrence in turbid waters (Ali et al, 1995(Ali et al, , 2011. Submersed macrophytes need, however, approximately 1-3% of the full sunlight spectrum (Wetzel, 2001).…”

“…Hornwort can hamper the phytoplankton growth in shallow eutrophic lakes, which contributes to the stabilization of the macrophyte-dominated state characterized by clear water (Gross et al, 1993;Mjelde and Faafeng, 1997). The species is very common in turbid, disturbed shallow water bodies, such as man-made reservoirs, due to its high tolerance to shade and disturbance (Ali et al, 1995(Ali et al, , 2011.…”