Monitoring wave-induced sediment resuspension

Abstract

The objective of this paper is to quantify resuspension and bed load transport of bottom sediments, induced by fast ferry wakes and wind waves near Aegna jetty, Tallinn Bay, using in situ measurements of waves, resuspension and optical properties of sea water. A new autonomous experimental set of two PAR-sensors, anchored into the sea bed, was used to measure the underwater irradiation. Wakes usually caused a rapid increase of the optical density of sea water by up to 50% from its background value. The total impact of fast ferry waves in terms of resuspended sediment concentration has not been substantially reduced compared to measurements in the past. However, wind waves apparently are the main driving force for both sediment resuspension and transport in 3 m deep water.

Comparing a 41-year model hindcast with decades of wave measurements from the Baltic Sea

“…The period of the ship wakes can exceed 10 s (e.g. Erm et al, 2009) and they showed up as visible narrow-banded peaks below 0.2 Hz in the wave buoy spectra, while they were completely missing from the spectra modelled by SWAN. Figure 4 (top right) shows that the highest peak periods were underestimated even when the significant wave height exceeded 0.5 m. For these higher sea states, e.g.…”

Shifts in Prey Selection and Growth of Juvenile Pikeperch (<i>Sander lucioperca</i>) over Half a Century in a Changing Lake Võrtsjärv

“…The historical data set on the diet and growth of juvenile pikeperch in Lake Võrtsjärv comprise three different time periods: the 1920s [12], 1950s [13] and 1960s-1970s [14][15][16]. The publications by Erm [13,14] and Haberman et al [16] give an overview of the diet of YOY pikeperch in Lake Võrtsjärv in summer and autumn.…”

“…The publications by Erm [13,14] and Haberman et al [16] give an overview of the diet of YOY pikeperch in Lake Võrtsjärv in summer and autumn. The autumn length data of pikeperch fry in Lake Võrtsjärv were published by Schneider [12], Erm [13,14], Kangur [15] and Haberman et al [16]. Altogether, the historical data set includes information on the diet of 551 and growth of 410 juvenile pikeperch.…”

“…The diet and growth of juvenile pikeperch have been studied several times since 1920 in a large shallow Lake Võrtsjärv [12][13][14][15][16][17]. Moreover, the probability of major shifts in the feeding modes of fish is especially high in shallow lakes [11] such as Lake Võrtsjärv.…”

“…In addition, an attempt was made to identify possible factors influencing the success of the pikeperch population in large shallow lakes. Therefore, studies since 1920 [12][13][14][15][16][17] on the diet, ontogenetic diet shift and growth of juvenile pikeperch were analysed to understand the long-term nature of pikeperch fry diet. This investigation concentrated on four different time periods: the 1920s, 1950s, 1960s-1970s and 2007-2010, as there have been significant shifts in living conditions and food supplies of juvenile pikeperch during those time periods.…”