This paper presents experimental measurements of beaching times for buoyant microplastic particles released, both in the pre-breaking region and within the surf zone. The beaching times are used to quantify cross-shore Lagrangian transport velocities of the microplastics. Prior to breaking the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity, regardless of particle characteristics. In the surf zone the Lagrangian velocities of the microplastics increase and become closer to the wave celerity. Furthermore, it is demonstrated that particles having low Dean numbers (dimensionless fall velocity) are transported at higher mean velocities, as they have a larger tendency to be at the free-surface relative to particles with higher Dean numbers. An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles, valid for both non-breaking and breaking irregular waves. The expression matches the present experiments well, in addition to two prior studies.
This paper presents a wave flume investigation of beaching times for buoyant microplastic particles dropped at various distance from the shoreline. The beaching times are used to quantify the cross-shore Lagrangian transport velocities of the microplastic particles. Results show that prior to breaking, there is little dependence on particle characteristics (e.g. their rise velocity), and the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity. In the surf zone the Lagrangian transport velocities of the microplastic particles increase significantly, becoming closer to the wave celerity. Additionally, particle characteristics become important, as particles with low Dean numbers (high rise velocity) have a greater tendency to be captured by surface rollers relative to particles with larger Dean numbers (lower rise velocity). An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles. The expression matches the present experiments well and is valid for both non-breaking and breaking irregular waves. These findings help in understanding the accumulation of microplastics at beaches due to the surf-zone processes, especially for buoyant particles.
Non-indigenous species (NIS) pose a major threat to biodiversity and the functioning and services of ecosystems. Despite their rapid spread in coastal waters worldwide, biotic invasions are widely disregarded in marine conservation planning. To guide conservation actions, a better understanding of the underlying mechanisms determining the success of NIS are therefore needed. Here we develop a combined modelling approach to identify the key drivers and community assembly processes determining the occurrence of invasive benthic invertebrates, using Danish coastal waters as a case study. To reflect factors affecting the introduction, establishment and spread of NIS throughout the area, we compiled long-term monitoring data on NIS, as well as information on commercial shipping, environmental conditions and estimates of larvae settling densities derived from drift model simulations informed by species traits. We then applied a set of species distribution models to identify the key drivers determining the occurrence of NIS. Our results demonstrate a significant positive effect of vessel activity, a negative effect of depth and bottom salinity, as well as a positive effect of the simulated settling densities on the probability of presence. Taken together, our results highlight the role of commercial shipping, habitat characteristics and passive advection of early-life stages on the presence of NIS. Our combined modelling approach provide improved process understanding on the key community assembly processes determining the presence of NIS and may serve to guide monitoring, management and conservation planning in order to limit future invasions and their negative consequences on coastal ecosystems.
Rapporter fra flere globale miljøinstitutioner, her
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under den internationale science-policy platform
om biodiversitet og økosystemtjenester (herefter
IPBES), understreger behovet for genopretning af
økosystemer (1,2). Den seneste globale IPBES-rap
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port fra maj 2019 peger således på, at forringelser
af økosystemer på land og i havet underminerer
livsgrundlaget for 3,2 milliarder mennesker. Gen
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opretning bliver fremhævet som en af de vigtig
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ste handlemuligheder for effektivt at begrænse
tabet af biodiversitet og forbedre livsgrundlaget
for os mennesker ved at imødegå forringelser for
en række økosystemtjenester. Det nuværende årti
2021-2030 er af UNEP udpeget til årtiet for genop
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retning med det formål at genetablere ødelagte
eller forarmede økosystemer verden over.
IPBES rapporterne dokumenterer, at biodiversi
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tetskrisen er en altomfattende og global udfor
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dring, og at krisen er på linje med klimakrisen. De
tiltagende klimaændringer er ligeledes en af ho
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vedårsagerne til tab af biodiversitet (2). Der er af
hensyn til begge kriser behov for, at der beskyttes
og genetableres velfungerende og uforstyrrede
økosystemer. Der bør derfor ske en national ud
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møntning af resultaterne fra de internationale aftaler baseret på den bedst tilgængelige viden.
We approach questions of Arctic marine resource economic development from the framework of environmental and resource economics. Shipping, fishing, oil and gas exploration and tourism are discussed as evolving industries for the Arctic. These industries are associated with a number of potential market failures which sustainable Arctic economic development must address. The varying scales of economic activity in the region range from subsistence hunting and fishing to actions by wealthy multinational firms. The ways in which interactions of such varied scales proceed will determine the economic futures of Arctic communities and the natural resources and ecosystems upon which they are based.