Agriculture ecosystems and environment pdf

Download Free PDF. Agriculture, Ecosystems and Environment. Anne Baily. A short summary of this paper. Significant rates of denitrification potentially enable strategic farming practices while protecting the water quality of local streams and rivers.

This could be done for example, by restricting land uses with unavoidable NO3- leaching losses to areas where the greatest denitrification potential exists in the underlying groundwater system.

Concurrently declining dissolved oxygen and NO3- concentrations can indicate that denitrification may be occurring along a groundwater flow path. Isotopic analysis of this NO3- can potentially provide evidence for the occurrence of denitrification and its quantification. In this study, shallow groundwater samples maximum 5 m below ground surface were taken from three locations within a small agricultural catchment in the Waikato region of New Zealand.

Results indicated that denitrification rates varied spatially, but interpretation was hampered by insufficiently understood flowpaths and extremely low concentrations of NO3- in reduced groundwater.

This indicated that the NO3- originated from multiple sources, which further hampered the quantification of denitrification. Stengera, T. E-mail: Juliet. Clague lincolnagritech. Stenger lincolnagritech. Clough lincoln. Significant rates of denitrification potentially enable strategic farming practices while 42 43 protecting the water quality of local streams and rivers. This could be done for example, by 44 45 restricting land uses with unavoidable NO3- leaching losses to areas where the greatest 46 47 48 denitrification potential exists in the underlying groundwater system.

Concurrently declining 49 50 dissolved oxygen and NO3- concentrations can indicate that denitrification may be occurring 51 52 along a groundwater flow path. Isotopic analysis of this NO3- can potentially provide evidence for 53 54 the occurrence of denitrification and its quantification. In this study, shallow groundwater 55 56 57 samples maximum 5 m below ground surface were taken from three locations within a small 58 59 agricultural catchment in the Waikato region of New Zealand.

This 19 20 indicated that the NO3- originated from multiple sources, which further hampered the 21 22 quantification of denitrification. Introduction 37 38 Nitrate NO3- contamination of freshwater resources is a global issue due to its impact on 39 40 potable water supplies and eutrophication of groundwater, streams and rivers Vitousek et al. Water quality guidelines set the maximum acceptable value MAV for NO3- in drinking 44 45 water at However, the trigger level at which ecological 46 47 change occurs in lowland streams and rivers is much lower 0.

In NZ, year-round grazing of intensively 55 56 managed pasture has resulted in many agricultural catchments having ground and surface 57 58 water with elevated NO3- concentrations MfE, In contrast, the direct leaching of 10 11 fertiliser-N is often negligible as application timing and rates are matched to meet plant demand 12 13 Ledgard et al. However, this approach does not take into account the flow paths 29 30 including their lag times and potential N transformations which may occur below the bottom of 31 32 the root zone in the vadose and saturated zones before the groundwater discharges into 33 34 surface water bodies.

There exists a research gap pertaining to the understanding and 35 36 quantification of denitrification in NZ groundwaters. Groffman et al. For example, a 47 48 49 decline in groundwater NO3- concentrations indicates denitrification is occurring; however, very 50 51 low NO3- concentrations are difficult to determine and the end product, N2, cannot be directly 52 53 determined in a groundwater sample, as groundwater already contains a significant amount of 54 55 N2 of atmospheric origin.

The mean stream water 43 44 transfer times Morgenstern et al. Instead, analysis of vertical 47 48 49 hydrochemistry profiles in the shallow groundwater system max. Materials and Methods 6 7 8 2. The predominant land use in the 15 km2 catchment is 18 19 20 intensive dairying, and has been for over 50 years. The average stocking rate in was 3. Topehaehae Site 28 29 The Topehaehae site comprised of a Typic Recent Gley Soil NZ soil classification Hewitt, 30 31 32 and was located on a river floodplain, derived of recent alluvial deposits.

The soil is characterised by a thin A horizon 0. During late 48 49 50 summer, the water table typically drops to approximately 1. An aquitard of dense silt material at 1. All wells in the catchment were 5 6 7 constructed of 50 mm diameter PVC pipe, with 0. Hydraulic 8 9 conductivities Ksat were derived from slug tests using the method of Bouwer and Rice 10 11 with values ranging from very fast rates of mm d-1 at 1.

These were installed horizontally in 3 sides of a pit excavated 26 27 28 to 1. Samplers were 31 32 installed in 6 replicates at three depths: 0. The soil is classified as a Typic Orthic Allophanic Soil 41 42 NZ soil classification Hewitt, and is a deep, well drained silt loam soil overlying a fine- 43 44 textured sandy clay loam. The soil has developed 45 46 from Holocene to late Pleistocene deposits of rhyolitic and andesitic volcanic ash Wilson, ; 47 48 49 Stevenson and Thornburrow, A positive response to the Childs test only occurred in the 50 51 lower part of the profile, approximately 4.

Water table minima typically occur in early autumn at approximately 54 55 3. Morrinsville Site 11 12 The Typic Orthic Granular Soil NZ soil classification Hewitt, found at the Morrinsville 13 14 site was characterised by a well drained clay loam soil overlying material that is less well 15 16 drained than the Kereone site.

The Morrinsville site was located approximately m from the 17 18 19 Kereone site and m from the stream Fig. These materials are strongly argillised Pleistocene 22 23 rhyolitic and andesitic volcanic ash layers which have formed pale coloured clay, often mottled 24 25 with bright orange iron concretions reflecting changes in redox conditions around the water table 26 27 28 Wilson, ; Stevenson and Thornburrow, A sharp redox boundary occurs between 3 29 30 and 3.

Figure 2 shows the positive 31 32 response to the Childs test in core samples taken in September , beginning at a depth of 33 34 3. The average minimum water table depth occurs in early autumn 2. Wells at the 37 38 39 Morrinsville site extended 2. Slug tests in 40 41 these wells revealed hydraulic conductivities ranging from slow 5 mm d-1 in 4. Sampling and Analytical Methods 48 49 50 2. Suction Tubes 51 52 Suction tubes sampling entailed removal of residual water followed by application of a 50 kPa 53 54 tension.

Although the methodology of Sigman et al. Four samplings 29 30 took place in early winter June or July while 6 sampling events occurred in late winter — early 31 32 spring August or September. Well Sampling 36 37 38 Standard well sampling procedure was to remove a water volume equivalent to 3 times the 39 40 standing water column Daughney et al.

However, some wells in the Toenepi catchment 41 42 recharged so slowly that wells were purged the day before sampling, and removal of more than 43 44 one standing water column was unfeasible. Low flow sampling methods Daughney et al. An 15 16 additional 50 mL sample was taken for isotopic analysis of NO Samples for isotopic analysis were stored frozen, shipped 26 27 28 cool and filtered to 0. Morgenstern et 41 42 al.

Results and Discussion 6 7 8 3. Nitrate Concentrations vs. The deepest well at the Topehaehae site 3. Therefore, the low 16 17 NO3- concentrations measured in these samples are unlikely to be a result of denitrification, but 18 19 20 rather they potentially reflect the lower N inputs into the system at the time of recharge 50 — 21 22 years ago. Topehaehae Site 35 36 37 3. Very high NO3- concentrations were measured at 0.

Under winter conditions temperatures of 7. In general, higher soil solution NO3- 54 55 concentrations were measured at all depths in early winter June and July , presumably due to 56 57 58 NO3- building up in the topsoil over summer when plant uptake was restricted by dry conditions 59 60 and subsequent leaching when drainage from the root zone of the pasture occurred.

A clear temporal change in isotopic 15 16 values occurred, with the August and September NO3- samples generally being more enriched 17 18 19 than those from June and July Fig. It is likely that this seasonal enrichment occurred 29 30 particularly at the 0. This is within the range previously reported 41 42 1.

Thus, NO3- measured at 0. This 28 29 assumed either no movement through the profile vertical or lateral , or that the source signal 30 31 was constant. Well Samples 11 In contrast to the suction tube samples, groundwater sampled from the wells at the Topehaehae 12 13 14 site had relatively stable NO3- and DO concentrations over time Fig.

This reflects 15 16 the nature of a well sample, as the vertically installed screens provide one composite sample for 17 18 a 0. Also, sampling the suction tubes required 24 25 application of a tension to the surrounding matrix, which presumably extracted a greater portion 26 27 of the water held more tightly in smaller pores than what occurred when sampling a well using a 28 29 pump.

The To well, screened 0. From this data, it is presumed that the 54 55 56 NO3- at 1. Tritium analysis showed that the To well 5 6 7 draws water that has a longer MTT than the To or To wells, with a MTT of 9 years, 8 9 compared to 1 year for the two shallower wells. It is therefore possible that some degree of 10 11 denitrification has occurred, since average NO3- and DO concentrations were low 0. It is likely 20 21 that measurement uncertainty was partly responsible for the spread of values as the samples 22 23 analysed were close to the isotopic detection limit 0.

Two factors 34 35 contributed to this. Firstly, as the well screen was 0. Secondly, the suction tube samplers take more of the small-pore water compared to 41 42 the well which primarily takes water freely moving in large pores, and conditions for 43 44 denitrification were likely to be more suitable in smaller pores, with longer contact time between 45 46 microbes, electron donors and NO Despite this, seasonal enrichment in the To well 47 48 49 provided the strongest indication of denitrification Fig.

Kereone Site 55 56 57 Only one sample was taken from the Ke well 3. Oxidised, NO3- -bearing groundwater was drawn at the Ke well, and 8 9 reduced groundwater with low NO3- concentrations at the Ke well. The average NO3- 10 11 concentration for the Ke well was 8. This is well within the range of values expected for NO3- derived 21 22 from soil N and manures Kendall, One sample, 29 30 from August Fig.

Mariotti et al. That denitrification rates were 42 43 rapid or that the small pores of an aquifer provided a sink for NO The 56 57 cause of the three isotopically depleted Ke samples is unknown Fig.

Zhang et al. It is unlikely that this conclusion applies to the Ke samples, 16 17 18 being both young and subject to recent agricultural practices. Therefore, it is assumed that 19 20 some contamination has resulted in these isotopically depleted values. Morrinsville Site 24 25 26 At the Morrinsville site well water samples had NO3- and DO concentrations that declined 27 28 strongly with increasing depth, with only the upper well at 2.

The well at 3. However, these 52 53 previous studies concluded that a significant vertical component of groundwater movement was 54 55 56 occurring, and that the oxidised water was the source of the NO3-, with denitrification occurring 57 58 within the vertical profile between the sampling depths of the oxidised and reduced 59 60 groundwater.

It is more likely that the majority of the water sampled at 3. Therefore, isotopic analysis cannot clarify whether denitrification has 14 15 contributed to the low NO3- concentrations measured in 3. The deepest well, at 16 17 18 4. Some of the isotopic 21 22 variability in the Mv samples may have been the result of measurement uncertainty as 23 24 many of these samples were close to analytical limitations 0. The benefits obtained by aquatic predatory birds from the availability of 19 fish, crayfish and other prey could be however thwarted by the increased contact with 20 agrochemical pollutants Ochoa et al.

This dominance of non-natives has probably increased in 3 recent times due to the establishment of fish species that are well adapted to occupy rice 4 fields dojo loach and stone moroko, see above. In addition, the invasive red swamp 5 crayfish was clearly a dominant species within rice fields, where an important number 6 of other non-native invertebrate taxa occur, notably gastropods and ostracods Oscoz et 7 al.

The high degree of invasion in rice fields could be related to the decline of 8 native taxa, such as the green frog Pelophylax perezi Santos and Llorente, Furthermore, the high availability of trophic resources in 12 rice fields, mainly in the form of non-native fish and crayfish, could be triggering 13 hyperpredation processes e.

Courchamp et al. Most non-native 18 fish species occupying the Ebro Delta are freshwater dwellers and their presence is 19 often associated with the freshwater inputs transported from the Ebro River to the rice 20 fields e. This disruption of 23 natural salinity regimes has been shown to favor invasive mosquitofish at the expense of 24 the endangered Spanish toothcarp Aphanius iberus Clavero et al. Aquatic organisms occupying rice fields in the 5 Ebro Delta have been important in the recovery of many waterbird species, but they are 6 mainly non-native species that interact negatively and through diverse pathways with 7 native aquatic fauna.

Besides focusing on yield, rice fields should be managed taking 8 into account their importance for the biota that inhabits them with a focus extending 9 beyond waterbirds , as well as their influence on surrounding natural systems. Garrido and N. An assessment of fish species assemblages in rice 20 fields in West Bengal, India: implications for management.

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Grey mullets Fam Mugilidae include at least three species: Mugil cephalus, Chelon labrosus and Liza ramada. Species codes are later used in Figures 3 and 5. Data for red swamp crayfish and other captured taxa are also shown. Mugilidae Grey mullets N - - Evolution along a year period of: i the area devoted to rice cultivation lines ; and ii rice yield crosses in south-western Europe, presented also separately for Portugal, Spain, France and Italy.

Results are shown for all fish captures A and separately for native B and introduces C fish species. Figure 3. Species codes are the same as those in table 1. Figure 4. Relationship between the number of occurrences of a species note the quadratic progression and the number of individuals of that species caught note the exponential progression , shown separately for the three environments analyzed.

Each dot represents a species in an environment, and thus a single species can be represented by up to three dots. Figure 5. A Size-structure of the most abundant fish species in the three surveyed habitats. Numbers in the X-axes of histograms show the range of sizes represented for each species and, in parenthesis, the magnitude of the size classes employed in mm.

The number of individuals measured is indicated by the number within each panel.