Hatfield J.L., Gandini A. (eds.) Nitrogen in the Environment

264 Nitrogen in the Environment

The newly adopted EU Water Framework Directive (WFD) aims at protecting

different water bodies to prevent further deterioration and to protect and enhance

the status of aquatic ecosystems ( European Parliament, 2000 ). The implementa-

tion of the WFD involves different steps where River Basin Authorities shall: (i)

perform an analysis of pressures and impacts (before 2005); (ii) develop monitor-

ing programs (before 2007); and (iii) implement mitigation strategies in the form

of River Basin Management Plans (before 2009). A good ecological quality should

be reached in surface water bodies before 2016 and this will in many river basins

demand further reductions in N loadings from especially diffuse sources.

The measures applied in selected European countries for combating N pollution

from point and diffuse sources are shown in Table 15 . Most countries have initiated

tertiary wastewater treatment and imposed regulations on manure restrictions and

storage.

In Denmark, the government has adopted five major Action Plans since the

early 1980s to reduce by 50% N pollution of the aquatic environment ( Table 16 ).

The Action Plan on the Aquatic Environment I from 1987 demanded N-removal at

all major sewage treatment plants ( ⬎ 15,000 PE). The regulations imposed to ensure

a reduction in N pollution from agriculture have been reiterated in all subsequent

Action Plans ( Table 15 ). Besides the multiple measures implemented, Denmark has

also adopted three other plans: (i) a Plan for Afforestation (1987) aimed to dou-

ble the forest area during the next 60–80 years (5,000 hectares per year); (ii) the

Strategy on Marginal Land (1987) aimed to restore 20,000 ha of former wetlands

over a 10 to 20 year period; and (iii) EU Set-Aside schemes. These plans will of

course also contribute to the reduction of the N pollution from farmland.

9 . CONCLUSIONS AND PERSPECTIVES

Concern about elevated N concentrations and loading to groundwater and surface

water in Europe has prompted the introduction of many reduction strategies at inter-

national, national, and local levels. Measures to reduce point source discharges of N

focus on tertiary treatment of urban wastewater as well as various key industries have

been implemented in most countries within the EU (see Tables 15 and 16 ).

Today, a high proportion of the total anthropogenic N loading to the aquatic

environment consists of N loading from agriculture (cf. Table 1 ). However, reduc-

ing the N input from agriculture is difficult for both technical and political reasons.

Measures may be introduced/implemented at the source to reduce the large N sur-

plus (as seen in many European countries, see Table 3 ). Another approach may be

to introduce transport measures to reduce the level of N before it reaches surface

and thus increase the N-removal potential along the routes followed by N from soil

to water.

The latter may be allowed by reinstating formerly drained lakes and wetlands in

which the potential for nitrate removal through the denitrification process normally

is high (see Tables 11–14 ). So far results obtained in Denmark and The Netherlands

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Table 15 .

Measures applied across Europe to combat nitrogen pollution.

Countries approach A B D DK E FIN F GR IRL I NL N P PL S UK

Point sources

UWWT tertiary

treatment

× × × × × × × × × × × ×

Industry – BAT × × × ×

Agriculture

Manure restrictions × × × × × × × × × × × × ×

Manure storage × × × × × × × × × × ×

Silage storage × × × × × × × ×

Fertilizer restrictions × × × × × × × × × × ×

Atmospheric input

Atmospheric sources × × × × × × × × × × ×

Industry – BAT × × × × × ×

A: Austria; B: Belgium; D: Germany; DK: Denmark; E: Spain; FIN: Finland; F: France; GR: Greece; IRL: Ireland;

I: Italy; NL: The Netherlands; N: Norway; P: Portugal; PL: Poland; S: Sweden; UK: United Kingdom.

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266 Nitrogen in the Environment

Table 16 .

Action Plans and their major elements adopted in Denmark to combat nitrogen

pollution from agriculture.

Action Plans

Year of adoption

Major implemented measures to

combat diffuse nitrogen pollution

NPO Action Plan 1985 Elimination of direct discharges

from farms

Livestock harmony on the farm

level

Action Plan on the

Aquatic Environment I

1987 9-month storage facility for slurry

65% winter green fields

Crop and fertilizer plans

Plan for sustainable

agricultural development

1991 Standard nitrogen fertilization

values for crops

Standard values for nitrogen in

animal manure

Required utilization of nitrogen in

animal manure (30–45%)

Fertilizer accounts at farm level

Action Plan on the

Aquatic Environment II

1998 Demands for an overall 10%

reduction of nitrogen application

to crops

Demands for catch crops

Demands for transforming 16,000 h a

farmland to wetlands

Reiterated demands for utilization

of nitrogen in animal manure

(40–55%)

Action Plan on the

Aquatic Environment III

2003 Halving of the Danish P surplus

before 2015

Reiterated demands for catch crops

and utilization of N in animal

manure

Establishment of 50,000 ha buffer

zones to reduce P loss from

agricultural fields

Demands for transforming 4,000 h a

of agricultural land to wetlands

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Nitrogen Transport and Fate in European Streams, Rivers, Lakes, and Wetlands 267

have shown that the potential for N-removal in lakes and freshwater wetlands is

high. In Denmark, the Second and Third Action Plans on the Aquatic Environment

(see Table 16 ) included the following initiative: to remove a total of 7,000 tons

N/year by rehabilitating 20,000 hectares of drained and otherwise reclaimed wet-

lands within 5 years.

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271

Chapter 10. Nitrogen Effects on Coastal Marine Ecosystems

J.R. Kelly

US Environmental Protection Agency (USEPA), Office of Research and

Development, National Health and Environmental Effects Research Laboratory,

Mid-Continent Ecology Division, Duluth MN, USA

Throughout the 20th century, a rapidly growing human population increased

the global circulation of nitrogen (N). In the United States and elsewhere, human

populations and activities have been disproportionately distributed towards coast-

lines, leading to markedly increased N inputs to coastal receiving waters. Nitrogen

inputs to coastal waters come from the land, from the sea, and from the air; because

of these multiple sources and the complexity of the N cycle, confident estimates

of total N loading to coastal systems are not routine. Ecological problems from

increasing inputs of N to coastal waters are well known and arise from stimulation

of algal growth. There is, however, a great diversity in coastal systems (estuaries,

small and large embayments, lagoons, open shelfwaters, and semi-enclosed coastal

seas) and vulnerability to increased N loading varies greatly. The combination of

uncertainties in characterization of loading and variability in response together have

hindered development of predictive N loading–ecological response relationships

and, in part, have engendered a case-by-case approach to defining protective limits

for N loading for coastal systems.

Evidence for a causal relationship between N loading and a variety of ecologi-

cal effects is strong. The general pattern for plankton responses to N inputs is non-

linear, with sharpest effects at lower loading rates and progressively shoaling to a

point where other factors (e.g., light, physical controls) become more limiting. Related

effects of increased N loading include depressed levels of dissolved oxygen (hypoxia

and anoxia) which injure or kill sensitive biological species; decline or elimination of

submerged aquatic vegetation (SAV) which provides critical habitat for some fish and

shellfish in shallow areas; promotion of certain algal species that are harmful because

they produce toxins; and other effects on coastal food webs and fisheries. Evidence

for effects comes from multiple observations in individual ecosystems over time,

comparative analyses across many systems with different loading rates, empirical and

simulation modeling, and from field-scale or mesocosm experiments. The progression

of ecological symptoms from increasing levels of N is generally predictable, but the

precise levels of loading that promote a certain effect vary across systems.

This chapter updates the 1st edition (2001) by reflecting on emerging 21st cen-

tury literature, which indicates this is a frenetic research area. Increasing N inputs to

Nitrogen in the Environment: Sources, Problems, and Management

J.L. Hatfield and R.F. Follett (Eds)

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272 Nitrogen in the Environment

the coastal zone have been confirmed in more places; symptoms of over-enrichment

continue to be reported worldwide and apparently are growing. Fundamental simi-

larities between coastal over-enrichment and lake eutrophication are broadly rec-

ognized, although finer details are still debated. We cannot yet scale the effects of

N loading to be predictive of effects, but this goal may be within our reach. Such a

scaling would consider: water residence time, system bathymetry and morphology,

water column stratification, regional biogeography and landscape setting, water

clarity and light penetration, food-web structure/history, and would recognize multi-

ple limiting nutrients. The emerging research perspective has matured to appreciate

how the problem is interwoven with a host of environmental and societal issues that

converge in the coastal zone.

1 . INTRODUCTION: NITROGEN AND COASTAL MARINE SYSTEMS

1

In the late 1960s the problem of nutrient inputs to freshwater systems, and sci-

entific debate about it, was reaching a peak. Although a critical volume on aquatic

eutrophication edited by Gene Likens (1972) did not exclude papers on marine and

estuarine systems, the principal focus was clear ( Likens 1972 , p. vi):

“I hope that the information provided in this volume may be useful to decision-

makers and thus contribute to a slowing of the eutrophication rate in our lakes

and streams . ”

Even before the freshwater decision-makers became fully focused on setting

limits on phosphorus (P) loading by a seminal experiment of Schindler (1974) ;

Ryther and Dunstan (1971) suggested that N played the more critical role in coastal

marine systems. We now know that there are low-salinity portions of some estuar-

ies, as well as some special individual marine cases, which are P-sensitive (e.g.,

Howarth, 1988 ; Krom et al., 1991 ; Doering et al., 1995 ; Malone et al., 1996 ;

Boynton, 2000 ). Similarly, there are various freshwater systems that are N-sensitive

(e.g., Elser et al., 1990 ). Moreover, it is clear that there are possible ecological con-

sequences of relative availability of silicate (Si) and N in coastal marine systems

(e.g., Officer and Ryther, 1980 ; Ryther and Officer, 1981 ; Doering et al., 1989 ;

Conley, 2000 ; Rabalais et al., 2000 ). But the overwhelming evidence, including

1

This chapter is only slightly revised from the 1st edition (2001). An “ Afterword

(2007) ” (Section 6) has been included to discuss recent research trends and per-

spectives on the problem in coastal systems.

The term “ coastal marine ” or “ coastal systems ” is used in this chapter as short-

hand for estuaries, shallow embayments, and lagoons, as well as more open near-

shore and shelfwater ecosystems along oceanic-terrestrial margins, as distinct from

similar coastal systems on large inland seas like the Great Lakes.

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Nitrogen Effects on Coastal Marine Ecosystems 273

observational evidence and controlled mesocosm experiments, confirms a central

role of N in establishing biological responses to nutrient loading in coastal waters

( Howarth, 1988 ; Doering et al., 1995 ; Oviatt et al., 1995 ; NRC, 2000 ).

Issues of shifted element ratios and their moderation of N effects are fascinating

and substantial (cf. Nixon et al., 1980 ; Nixon, 1981 ; Doering et al., 1989 ; Rabalais

et al., 2000 ; Seitzinger, 2000 ). But it is challenging enough to review effects relat-

ing to different levels of N, which is the principal focus of this chapter.

Nitrogen circulation through the global environment has been growing dramati-

cally ( Vitousek et al., 1997 ). Delivery via rivers to receiving systems has increased

greatly in the last half of the 20th century (e.g., Howarth et al., 1996 ; CENR, 2000 ;

and other chapters in this volume). Unlike P, there is a significant atmospheric path-

way for N. Local- to longer-range atmospheric transport and deposition to many

regions, including coastal waters, has risen as a consequence of fossil fuel burning,

agricultural practices, and other human activities. Riverine and atmospheric enrich-

ments, combined with burgeoning coastal zone populations of humans and their asso-

ciated land use changes and wastewater releases, make coastal systems a frontline

receiving system for much of the enormous global N enrichment experiment now in

progress. What is happening in coastal ecosystems and what do we expect to happen

if N loads continue to rise?

In the same volume cited above ( Likens, 1972 ), Clifford Mortimer gave some

opening comments (p. viii), which provide a fabric for this chapter:

“Although the analogy can not be pressed too far, it will be noted that the

research aimed toward cure of cancer–like eutrophication, a problem of

unwanted proliferation of cells–devotes considerably more effort and resources

to the study of cell processes than to description of symptoms. Until now, the

reverse has been the case in eutrophication research.”

It is not that recognition of coastal marine eutrophication had its genesis in

1971; indeed it began at least at the latter part of the 19th century (cf. historical

perspectives of Nixon et al., 1986 ; Nixon, 1992, 1998 ). But the paper of Ryther and

Dunstan (1971) , with work started much earlier by Ryther (1954) , was an epiph-

any which did spur an emphasis on N research that has continued and increased for

the last three decades ( Nixon, 1995 ). At the beginning of the 21st century, we now

have very little problem identifying Mortimer ’ s “ symptoms ” of N overenrichment,

due to innumerable related conferences, symposia, and associated volumes, articles,

books, and virtually uncountable numbers of greyer-literature reports ( Lauff, 1967 ;

NAS, 1969 ; Nielson and Cronin, 1981 ; Boynton et al., 1982 ; Carpenter and Capone,

1983 ; Chesapeake Bay Program, 1983 ; Kennedy, 1984 ; Valiela, 1984 ; Rosenberg,

1985 ; Nixon et al., 1986 ; Kullenberg, 1986a ; Howarth, 1988 ; Nixon, 1988 ;

GESAMP, 1990 ; Elliott and Ducrotoy, 1991 ; Vollenweider et al., 1992 ; NRC,

1993 ; Nixon, 1995 ; Bricker and Stevenson, 1996 ; Nixon et al., 1996 ; Anderson and

Garrison, 1997 ; NRC, 2000 ; Hobbie, 2000 ). At core, symptoms are similar to those

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Hatfield J.L., Gandini A. (eds.) Nitrogen in the Environment

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