TY - JOUR
TI - Productivity driven by Tana river discharge is spatially limited in
Kenyan coastal waters
AU - Mutia, Damaris
AU - Carpenter, Stephen
AU - Jacobs, Zoe
AU - Jebri, Fatma
AU - and Kamau, Joseph
AU - Kelly, Stephen J.
AU - Kimeli, Amon
AU - Langat,
AU - Philip Kibet
AU - Makori, Amina
AU - Nencioli, Francesco
AU - Painter,
AU - Stuart C.
AU - Popova, Ekaterina
AU - Raitsos, Dionysios
AU - Roberts,
AU - Michael
JO - OCEAN & COASTAL MANAGEMENT
PY - 2021
VL - 211
TODO - null
SP - null
PB - Elsevier Sci Ltd, Exeter, United Kingdom
SN - 0964-5691
TODO - 10.1016/j.ocecoaman.2021.105713
TODO - Tana River; Chlorophyll-a; Western Indian Ocean; Remote sensing
TODO - The Tana River is the longest river system in Kenya (-1000 km) and
contributes - 50% of the total river discharge to Kenyan coastal
waters. The river discharges significant amounts of nutrients and
sediments, reaching -24,000 tons per day during the rainy season
(March-April), into Ungwana Bay (North Kenya Banks). The bay is an
important habitat for high-value Panaeid prawn species which sustain
important small-scale fisheries, semi-industrial bottom trawl prawn
fisheries, and is the livelihood mainstay in the surrounding counties.
In this study we analysed 20 years of satellite-derived chlorophyll-a
observations (Chl-a, an index of phytoplankton biomass), along with in
situ river discharge and rainfall data, to investigate if the Tana River
discharge is a major driver of local phytoplankton biomass in Ungwana
Bay and for the neighbouring Kenyan shelf. We find that during the rainy
inter-monsoon (March-April), a significant positive relationship (r =
0.63, p < 0.0001) exists between river discharge and phytoplankton
biomass. There is a clear time-lag between rainfall, river discharge
(1-month lag) and local chlorophyll biomass (2-months lag after
discharge). Unlike offshore waters which exhibit bi-annual chl-a peaks
(0.22 mg m3 in February, and 0.223 mg m3 in August/September), Ungwana
Bay displays a single peak per annum in July (2.51 mg m- 3), with
indications that river discharge sustains phytoplankton biomass for
several months. Satellite-derived observations and Lagrangian tracking
simulations indicate that higher Chl-a concentrations remain locally
within the bay, rather than influencing the broader open waters of the
North Kenya Banks that are mainly impacted by the wider oceanic
circulation.
ER -