ENVR101 Nitrogen and Phosphorus Cycle

Sampling indicates that up to a third of wells in Canterbury exceed World Health Organization (WHO) guidelines for safe drinking water which is concerning for public health.
Primary cause: Conversion of Canterbury Plains for dairying, leading to nitrate runoff from cattle effluent. Intensive agricultural practices exacerbate the issue.
Regulations around Christchurch protect the city's drinking water supply, indicating a localized awareness and management strategy.

Overland flow: Direct runoff into waterways. Fencing helps by preventing livestock access, but isn't completely effective due to factors like heavy rainfall.
Seepage into groundwater: Effluent seeps into the ground, travels in shallow groundwater, and resurfaces near the coast, resulting in widespread contamination.
Smaller rivers and groundwater sources have higher nitrate concentrations, posing greater risks to local ecosystems and human populations.
Lake Ellesmere is experiencing decline in health due to nitrates flowing down rivers, highlighting ecological damage.

Eutrophication is when too much nitrogen fertilizes the water, leading to ecological imbalance.
Healthy waterways have macrophytes (water weeds) leading to high oxygen content, which supports diverse aquatic life.
Excess fertilization leads to a surge in plant growth, followed by plant decay and oxygen depletion, creating dead zones.
Macrophytes are replaced by cyanobacteria (toxic blue-green algae), which produce harmful toxins.
Autotrophic systems (photosynthesis-driven) change to heterotrophic systems (bacteria/fungi-dominated), altering the food web.

New Zealand has set a limit on synthetic nitrogen use at 190 kg/hectare/year from 2022, aiming to reduce environmental impact.
New Zealand drinking standard: maximum acceptable value of 50 mg/L nitrate = 11.3 mg/L nitrogen, ensuring safe potable water.
High nitrogen levels interfere with breathing and can cause blue baby syndrome, posing serious health risks, especially to infants.

Lake Forsyth regularly experiences cyanobacteria blooms, impacting recreational use and ecological health.
Questions to consider:-
- Has the lake's environment changed over time?
- Is the change human-induced?

High chlorophyll a levels linked to blue-green algae surges, indicating eutrophic conditions.
Eutrophication peaks during January-April when water levels are low, temperatures are high, and circulation is minimal, promoting algal growth.

Analyzing lake cores helps determine historical conditions, providing insights into past environmental states.
Radiocarbon dating of seeds determines the age of sediment layers, creating a timeline of environmental changes.
Analysis includes chlorophyll a levels and midge (Chironomidae) head capsules, serving as bioindicators of water quality.
Coronimus zealandica indicates poor water quality, useful for assessing environmental degradation.
Transfer functions convert head capsule percentages into nutrient levels, quantifying past nutrient concentrations.
Data helps establish baseline conditions before European and Maori arrival, offering a reference point for assessing current impacts.

Oceans have more nitrogen fixation than land, primarily in the deep ocean, playing a crucial role in global nitrogen balance.
Nitrogen flux from land is significant but not huge, affecting coastal ecosystems.
Deep oceans have 10x proportions than coastal regions, influencing marine productivity.
Natural release of nitrous oxide, a potent greenhouse gas.
Bacteria mediate nitrogen cycling in the ocean (similar to soil), driving key biogeochemical processes.
N2 is converted to ammonium, hydroxylamine, nitrite, and nitrate through various bacterial pathways.
Deeper in the ocean, nitrate converts back to nitrous oxide and ammonium, completing the cycle.

Oxygen is highest in surface waters; deep waters are anoxic or oxygen-poor, impacting nutrient distribution.
Top of the ocean produces nitrates (fertilizers for plants and animals), supporting marine food webs.
Bottom of the ocean converts nitrogen into anoxic forms (nitrogen gas, nitrites), removing bioavailable nitrogen.
Reduced nitrogen stored in the deep ocean with a closed cycle at the top, maintaining nutrient balance.

High chlorophyll a (biological activity/photosynthesis) is concentrated around the poles and by land, indicating regions of high productivity.
Algal blooms occur in the North Pacific, North Atlantic, and Southern Ocean, affecting marine ecosystems.
Nutrient maxima (phosphorus, nitrogen, silica) found in the Southern Ocean and North Pacific, supporting algal growth.
Algal blooms are directly related to fresh supplies of nitrogen and phosphorus, highlighting nutrient limitation.

Antarctic bottom water and North Atlantic deepwater are generated, leading to upwelling of nutrients, distributing nutrients globally.
Upwelling in the North Pacific and off the coast of Peru, fueling productive fisheries.
Blooms are related to areas of fresh supplies, connecting ocean dynamics to biological activity.

Nitrous oxide contributes 7% to global greenhouse gas impact, exacerbating climate change.
One molecule of nitrous oxide has the greenhouse gas efficiency of 300 molecules of carbon dioxide, making it a potent greenhouse gas.
Main source: exhaust fumes and agricultural practices.
Estimated that about 20% of New Zealand's greenhouse gas emissions are from nitrous oxide, posing environmental challenges.

Nitrogen is common but inaccessible in its stable N2 form, requiring conversion for biological use.
Bacteria are critical for nitrogen uptake and conversion, driving the nitrogen cycle.
Human activity has greatly modified the nitrogen cycle through fertilizer production, leading to imbalances.
Nitrogen use causes eutrophication, impacting water quality.
Nitrous oxides are important greenhouse gases, contributing to climate change.

Fertilizer contains nitrogen, phosphorus, and potassium (NPK), essential for plant growth.
Potassium has little impact on plants, primarily used for structural support.
Phosphorus and nitrogen work in tandem, enhancing plant productivity.
Weathered away and depleted in old soils, limiting plant growth.
Traditional sources of phosphorus: guano, Nauru (now depleted), highlighting resource depletion.
Current primary source: apatite (calcium phosphate from Morocco), raising sustainability concerns.
Phosphorus is part of ATP/ADP energy exchange, crucial for respiration and energy transfer in cells.