changes has to take into account the effects of distant
forcing, i.e., global climate change, the interaction of
external forcing and geographic settings can derive a different and sometimes unforeseen driving force at local
and/or regional scale. The natural forcings should also
include change in atmospheric depositions and riverine
influx, however, with consideration of the respective
effects of the anthropogenic perturbations. In temperate
and high-latitude regions, the recurring seasonal changes
and their considerable interannual variability are the most
important factors in shaping the biogeochemical cycles of
materials.
Since the coastal ocean is adjacent to the continental
and/or landmass (e.g., islands), the “biogeochemical
cycles” in this region is also modulated by the human
being activities in the watersheds and in the ocean-side
(LOICZ, 2005). Change in land-use and hydraulic engineering (e.g., damming the river) over the watersheds
can dramatically modify the seaward transport of
weathering products and pollutants, including riverine
flux as well as groundwater discharge and their variability
at seasonal and interannual scales. For instance, the terrestrial sediment load has been reduced by more than 50 %
and the nutrient fluxes increased by up to twofold for some
of the top world rivers over the last several decades
(Boesch, 2002; Syvitski et al., 2005). Other examples
include the reclamation for arable land in the coastal zone
for aquaculture, e.g., shrimp ponds that destroy the wetland, and because of expansion of urbanization, particularly so in the developing countries. The global
overfishing problem can have a “top-down” effect on the
energy and material flow in ecosystems by removing top
predators as well as herbivores thus disturbing interactions
in the entire food web (GLOBEC, 1997). Moreover, eutrophication in the coastal environment can exert a negative
impact on the ecosystem through “bottom-up” effects that
modify macronutrients and their molar ratios and hence
alter the community structure of phytoplankton
(GEOHAB, 2001).
How and to what extent the natural and anthropogenic
forcings interact have a determining effect on the biogeochemical cycles in the coastal ocean, which in turn modulates the structure and function of ecosystems. This is
probably why the coastal biogeochemical cycles have significant varying temporal and spatial dimensions and
accordingly the research and results often have a casespecific nature.
Machinery of the coastal biogeochemical cycles
The coastal environment exhibits the transit zone between
the landmass and the open ocean where the properties of
land and ocean are strongly modulated. Thus, strong gradients exist for hydrographic parameters (i.e., salinity
and temperature), chemical properties (e.g., major and
trace element concentrations), turbidity and profiles of
photosynthetically available radiation, as well as for the
composition of organisms.
Dynamics of biogeochemical cycles of the
coastal ocean
The coastal biogeochemical cycles incorporate dynamic
processes that include the major pathways of chemical elements between biotic and abiotic compartments and variability of source versus sink terms in the euphotic
waters, where the tiny phytoplankton and marine algae
use the energy from solar radiation to fix carbon dioxide
from atmosphere and change it to chemical energy of
organisms, releasing oxygen:
CO 2 þ H 2 O ! CH 2 O þ O 2
where the symbol “CH 2 O” stands for a simplified composition of organic matter. This photosynthesis fuels the biogeochemical cycles and energy flow in the entire water
column and through the entire food web. Along with photosynthesis, macronutrients such as N, P, Ca, and Si, and
about further 30 minor and trace elements such as As,
Cd, Co, Cu, Fe, Mn, Mo, Se, V, Zn, etc. that are biologically essential, are also taken up by phytoplankton
(Figure 1). Particularly C, N, P, and O 2 are incorporated
and remineralized in a relatively fixed molar quota, the
so-called Redfield ratio: C:N:P:O ¼ 106:16:1:138
(Redfield et al., 1963; Moral et al., 2003). Chemical elements can be either incorporated as components for soft
organic matter or used to form skeletons and cell wall of
organisms (GEOTRACES, 2006). Nutrients and trace elements used by the organisms in photosynthesis can be supplied from external sources, like land-source input via
rivers and groundwater discharge, atmospheric wet and
dry depositions, release through the sediment-water interface, advective transport, and upwellings from open
ocean. Generally speaking, all nutrient supply from outside the euphotic zone, which includes nutrients enriched
in surface waters during the nongrowth period of phytoplankton, is defined as “new production,” which maintains
the sustainable food production of ecosystem (e.g., fishery); in contrast phytoplankton uptake of nutrients stemming from remineralization in the food webs of euphotic
zone is referred to as “regenerated production” (Dugdale
and Goering, 1967).
The organic matter formed in photosynthesis is in part
transferred to zooplankton and then through herbivores
and carnivores up to the top predators in the food web.
Organic matter escaping from water column remineralization sinks eventually to the seafloor as also do inorganic biogenic materials (e.g., carbonate skeletons and
silicate shells) that survive dissolution in the water column. The whole journey from the carbon fixation by photosynthesis in surface waters until the organic matter
deposition to the sea bottom is referred to as “biological
pump” in Global Change Science.
Since the mid-1970s, the significance of microbial loop
has been recognized in the ecosystem functioning that
complements the traditionally defined “food chain,” i.e.,
phytoplankton via zooplankton to fish, playing an important qualitative and quantitative role in the
COASTAL BIO-GEOCHEMICAL CYCLES
95
forcing, i.e., global climate change, the interaction of
external forcing and geographic settings can derive a different and sometimes unforeseen driving force at local
and/or regional scale. The natural forcings should also
include change in atmospheric depositions and riverine
influx, however, with consideration of the respective
effects of the anthropogenic perturbations. In temperate
and high-latitude regions, the recurring seasonal changes
and their considerable interannual variability are the most
important factors in shaping the biogeochemical cycles of
materials.
Since the coastal ocean is adjacent to the continental
and/or landmass (e.g., islands), the “biogeochemical
cycles” in this region is also modulated by the human
being activities in the watersheds and in the ocean-side
(LOICZ, 2005). Change in land-use and hydraulic engineering (e.g., damming the river) over the watersheds
can dramatically modify the seaward transport of
weathering products and pollutants, including riverine
flux as well as groundwater discharge and their variability
at seasonal and interannual scales. For instance, the terrestrial sediment load has been reduced by more than 50 %
and the nutrient fluxes increased by up to twofold for some
of the top world rivers over the last several decades
(Boesch, 2002; Syvitski et al., 2005). Other examples
include the reclamation for arable land in the coastal zone
for aquaculture, e.g., shrimp ponds that destroy the wetland, and because of expansion of urbanization, particularly so in the developing countries. The global
overfishing problem can have a “top-down” effect on the
energy and material flow in ecosystems by removing top
predators as well as herbivores thus disturbing interactions
in the entire food web (GLOBEC, 1997). Moreover, eutrophication in the coastal environment can exert a negative
impact on the ecosystem through “bottom-up” effects that
modify macronutrients and their molar ratios and hence
alter the community structure of phytoplankton
(GEOHAB, 2001).
How and to what extent the natural and anthropogenic
forcings interact have a determining effect on the biogeochemical cycles in the coastal ocean, which in turn modulates the structure and function of ecosystems. This is
probably why the coastal biogeochemical cycles have significant varying temporal and spatial dimensions and
accordingly the research and results often have a casespecific nature.
Machinery of the coastal biogeochemical cycles
The coastal environment exhibits the transit zone between
the landmass and the open ocean where the properties of
land and ocean are strongly modulated. Thus, strong gradients exist for hydrographic parameters (i.e., salinity
and temperature), chemical properties (e.g., major and
trace element concentrations), turbidity and profiles of
photosynthetically available radiation, as well as for the
composition of organisms.
Dynamics of biogeochemical cycles of the
coastal ocean
The coastal biogeochemical cycles incorporate dynamic
processes that include the major pathways of chemical elements between biotic and abiotic compartments and variability of source versus sink terms in the euphotic
waters, where the tiny phytoplankton and marine algae
use the energy from solar radiation to fix carbon dioxide
from atmosphere and change it to chemical energy of
organisms, releasing oxygen:
CO 2 þ H 2 O ! CH 2 O þ O 2
where the symbol “CH 2 O” stands for a simplified composition of organic matter. This photosynthesis fuels the biogeochemical cycles and energy flow in the entire water
column and through the entire food web. Along with photosynthesis, macronutrients such as N, P, Ca, and Si, and
about further 30 minor and trace elements such as As,
Cd, Co, Cu, Fe, Mn, Mo, Se, V, Zn, etc. that are biologically essential, are also taken up by phytoplankton
(Figure 1). Particularly C, N, P, and O 2 are incorporated
and remineralized in a relatively fixed molar quota, the
so-called Redfield ratio: C:N:P:O ¼ 106:16:1:138
(Redfield et al., 1963; Moral et al., 2003). Chemical elements can be either incorporated as components for soft
organic matter or used to form skeletons and cell wall of
organisms (GEOTRACES, 2006). Nutrients and trace elements used by the organisms in photosynthesis can be supplied from external sources, like land-source input via
rivers and groundwater discharge, atmospheric wet and
dry depositions, release through the sediment-water interface, advective transport, and upwellings from open
ocean. Generally speaking, all nutrient supply from outside the euphotic zone, which includes nutrients enriched
in surface waters during the nongrowth period of phytoplankton, is defined as “new production,” which maintains
the sustainable food production of ecosystem (e.g., fishery); in contrast phytoplankton uptake of nutrients stemming from remineralization in the food webs of euphotic
zone is referred to as “regenerated production” (Dugdale
and Goering, 1967).
The organic matter formed in photosynthesis is in part
transferred to zooplankton and then through herbivores
and carnivores up to the top predators in the food web.
Organic matter escaping from water column remineralization sinks eventually to the seafloor as also do inorganic biogenic materials (e.g., carbonate skeletons and
silicate shells) that survive dissolution in the water column. The whole journey from the carbon fixation by photosynthesis in surface waters until the organic matter
deposition to the sea bottom is referred to as “biological
pump” in Global Change Science.
Since the mid-1970s, the significance of microbial loop
has been recognized in the ecosystem functioning that
complements the traditionally defined “food chain,” i.e.,
phytoplankton via zooplankton to fish, playing an important qualitative and quantitative role in the
COASTAL BIO-GEOCHEMICAL CYCLES
95