204
S. Sánchez-Carrillo et al.
15.1 Introduction
Ecosystem evaluation and management consistently requires measures that monitor the present state of a system
and characterize its rate of change in response to exogenous
disturbances. The biological symptoms of eutrophication in
wetlands appear to be similar to those in shallow lakes but
the ecosystem biogeochemical responses may be different
(Reddy and Delaune 2008; Sánchez-Carrillo and Angeler
2010). The main obstacles for modeling eutrophication
in wetlands to find good indicators of ecosystem changes
derive from the use of biological communities and water
quality standards inherited from the classical studies on
eutrophication in temperate lakes. In lakes, phytoplankton
biomass increases when the nutrient limiting supply rises
(i.e., algal blooms). In shallow lakes, changes are consistent
with predictions made by alternative state theory (Scheffer
et al. 1993) and the trophic cascade concept (Carpenter and
Kitchell 1993): increased nutrient and water turbidity levels, shift the ecosystem from submerged macrophyte dominance to phytoplankton dominance (e.g., Whillans 1996;
Chow-Fraser 1998; Álvarez-Cobelas et al. 2001). In wetlands, considering the wide disparity between ecosystem
types (e.g., only taking into account hydrogeomorphological aspects; Brinson 1993) and since wetlands are known to
function as nutrient transformers in the landscape (Phillips
1996; Gunatilaka 1991; Sánchez-Carrillo and Álvarez-Cobelas 2001) the response of phytoplankton and submerged
charophyte communities to nutrient enrichment does not
follow a clear pattern.
Nutrient enrichment in wetlands has been shown to influence all trophic levels and its effects include changes
in species abundance, replacement, biodiversity loss, and
shifts in community structure and composition (Piceno and
Lovell 2000; Álvarez-Cobelas et al. 2001; Guntenspergen
et al. 2002; Liston et al. 2008). Abiotic shifts induce biotic
changes and these, in turn, lead to complex feedback effects
on ecosystem metabolism. As nutrient loading increase, biogeochemical processes in wetlands are altered, changing
nutrient concentrations in water and soil and, hence, nutrient fluxes among compartments. These ecosystem-wide
changes modify conditions within the wetland and alter the
physical and chemical environment. The addition of limiting
nutrients to wetland ecosystems increases primary productivity and stimulates microbial processes. Organic matter decomposition and nutrient cycling in wetlands depend on the
chemical and physical composition of soil, microbial activity
and nutrient availability (Wright et al. 2009). Nutrient enrichment has been shown to generate significant alterations
for wetland structure and function (Davis et al. 2003) and
induce changes in soil physicochemical and microbiological
characteristics that may then serve as effective indicators of
nutrient enrichment (Corstanje and Reddy 2006).
Microbial communities play a key role in nutrient cycling and organic matter degradation in wetland systems.
Wetland soils are relatively rich in functional microbial
communities that are capable of utilizing a wide range of
electron acceptors, such as O 2 , NO 3
− , Fe
3+
, SO 3
− , and CO 2
(D’Angelo and Reddy 1999; Wright and Reddy 2001a). Environmental and resource conditions form the fundamental
forces that control the microbial community size and its
dynamics (Corstanje et al. 2007). In wetlands, microbial
communities have been shown to respond to nitrogen (N)
and phosphorus (P) enrichment, increasing litter decomposition rates (Davis 1991; DeBusk and Reddy 1998). Microbial responses to enhanced nutrient levels are also reflected
in changes on indices of microbial activity, such as respiratory activities (White and Reddy 2001) and extracellular
activities (Sinsabaugh and Moorhead 1994; Corstanje et al.
2007). Eutrophication in marsh systems has also been associated with increases in microbially mediated C, N, and P
turnover rates (Reddy et al. 1999), and increases in soil MB
Content as well (Qualls and Richardson 1995). Experimental addition of N and P to natural systems (Newbold et al.
1983) and to enrichment mesocosm experiments (Qualls
and Richardson 2000; Newman et al. 2001) have produced
significant increases on microbial activity, primarily as a
function of their status as limiting factors in the systems
under observation. Monitoring the variables associated
with the microbial ecophysiology in response to external
disturbances, as well as establishing the baseline of the
endogenous environment, has provided basic information
of changes on ecosystem functioning related with nutrient
enrichment (Corstanje et al. 2007). The aim of this chapter
is to provide an overview on the use of microbial communities as indicators of wetland ecosystem changes related with
eutrophication processes. Since wetlands play a key role on
the terrestrial nutrient cycling, this chapter is focused to the
effects of nutrient enrichment on both biogeochemical and
microbial processes as a reflection of changes in ecosystem functioning. We selected a set of microbial community
response measures known to be sensitive to nutrient enrichment in aquatic systems, such as extracellular enzyme
activities (Prenger and Reddy 2004), respiratory activities
(DeBusk and Reddy 1998; Qualls and Richardson 2000),
MBC, N and P, and microbially mediated N and P turnover
rates (Reddy et al. 1999). These measures, and their derivatives or simple combinations as well, have been used to
characterize individually the microbial community physiological response to changes in its environment (Anderson
and Domsch 1990; Sinsabaugh et al. 1997). The focus of
this review is to generate an overall assessment of the effectiveness of the microbial community and its ecophysiology as indicators of ecological perturbation generated by
nutrient enrichment in wetlands, with a specific emphasis
on the microbially mediated organic matter decomposition
S. Sánchez-Carrillo et al.
15.1 Introduction
Ecosystem evaluation and management consistently requires measures that monitor the present state of a system
and characterize its rate of change in response to exogenous
disturbances. The biological symptoms of eutrophication in
wetlands appear to be similar to those in shallow lakes but
the ecosystem biogeochemical responses may be different
(Reddy and Delaune 2008; Sánchez-Carrillo and Angeler
2010). The main obstacles for modeling eutrophication
in wetlands to find good indicators of ecosystem changes
derive from the use of biological communities and water
quality standards inherited from the classical studies on
eutrophication in temperate lakes. In lakes, phytoplankton
biomass increases when the nutrient limiting supply rises
(i.e., algal blooms). In shallow lakes, changes are consistent
with predictions made by alternative state theory (Scheffer
et al. 1993) and the trophic cascade concept (Carpenter and
Kitchell 1993): increased nutrient and water turbidity levels, shift the ecosystem from submerged macrophyte dominance to phytoplankton dominance (e.g., Whillans 1996;
Chow-Fraser 1998; Álvarez-Cobelas et al. 2001). In wetlands, considering the wide disparity between ecosystem
types (e.g., only taking into account hydrogeomorphological aspects; Brinson 1993) and since wetlands are known to
function as nutrient transformers in the landscape (Phillips
1996; Gunatilaka 1991; Sánchez-Carrillo and Álvarez-Cobelas 2001) the response of phytoplankton and submerged
charophyte communities to nutrient enrichment does not
follow a clear pattern.
Nutrient enrichment in wetlands has been shown to influence all trophic levels and its effects include changes
in species abundance, replacement, biodiversity loss, and
shifts in community structure and composition (Piceno and
Lovell 2000; Álvarez-Cobelas et al. 2001; Guntenspergen
et al. 2002; Liston et al. 2008). Abiotic shifts induce biotic
changes and these, in turn, lead to complex feedback effects
on ecosystem metabolism. As nutrient loading increase, biogeochemical processes in wetlands are altered, changing
nutrient concentrations in water and soil and, hence, nutrient fluxes among compartments. These ecosystem-wide
changes modify conditions within the wetland and alter the
physical and chemical environment. The addition of limiting
nutrients to wetland ecosystems increases primary productivity and stimulates microbial processes. Organic matter decomposition and nutrient cycling in wetlands depend on the
chemical and physical composition of soil, microbial activity
and nutrient availability (Wright et al. 2009). Nutrient enrichment has been shown to generate significant alterations
for wetland structure and function (Davis et al. 2003) and
induce changes in soil physicochemical and microbiological
characteristics that may then serve as effective indicators of
nutrient enrichment (Corstanje and Reddy 2006).
Microbial communities play a key role in nutrient cycling and organic matter degradation in wetland systems.
Wetland soils are relatively rich in functional microbial
communities that are capable of utilizing a wide range of
electron acceptors, such as O 2 , NO 3
− , Fe
3+
, SO 3
− , and CO 2
(D’Angelo and Reddy 1999; Wright and Reddy 2001a). Environmental and resource conditions form the fundamental
forces that control the microbial community size and its
dynamics (Corstanje et al. 2007). In wetlands, microbial
communities have been shown to respond to nitrogen (N)
and phosphorus (P) enrichment, increasing litter decomposition rates (Davis 1991; DeBusk and Reddy 1998). Microbial responses to enhanced nutrient levels are also reflected
in changes on indices of microbial activity, such as respiratory activities (White and Reddy 2001) and extracellular
activities (Sinsabaugh and Moorhead 1994; Corstanje et al.
2007). Eutrophication in marsh systems has also been associated with increases in microbially mediated C, N, and P
turnover rates (Reddy et al. 1999), and increases in soil MB
Content as well (Qualls and Richardson 1995). Experimental addition of N and P to natural systems (Newbold et al.
1983) and to enrichment mesocosm experiments (Qualls
and Richardson 2000; Newman et al. 2001) have produced
significant increases on microbial activity, primarily as a
function of their status as limiting factors in the systems
under observation. Monitoring the variables associated
with the microbial ecophysiology in response to external
disturbances, as well as establishing the baseline of the
endogenous environment, has provided basic information
of changes on ecosystem functioning related with nutrient
enrichment (Corstanje et al. 2007). The aim of this chapter
is to provide an overview on the use of microbial communities as indicators of wetland ecosystem changes related with
eutrophication processes. Since wetlands play a key role on
the terrestrial nutrient cycling, this chapter is focused to the
effects of nutrient enrichment on both biogeochemical and
microbial processes as a reflection of changes in ecosystem functioning. We selected a set of microbial community
response measures known to be sensitive to nutrient enrichment in aquatic systems, such as extracellular enzyme
activities (Prenger and Reddy 2004), respiratory activities
(DeBusk and Reddy 1998; Qualls and Richardson 2000),
MBC, N and P, and microbially mediated N and P turnover
rates (Reddy et al. 1999). These measures, and their derivatives or simple combinations as well, have been used to
characterize individually the microbial community physiological response to changes in its environment (Anderson
and Domsch 1990; Sinsabaugh et al. 1997). The focus of
this review is to generate an overall assessment of the effectiveness of the microbial community and its ecophysiology as indicators of ecological perturbation generated by
nutrient enrichment in wetlands, with a specific emphasis
on the microbially mediated organic matter decomposition