किस प्रकार के उर्वरक के अत्यधिक उपयोग से भूजल में नाइट्रेट संदूषण (nitrate contamination) होता है?

Prolonged exposure to extreme cold temperatures may result in tissue damage known as frostbite, which is categorized as a:

In the context of ecosystem energy dynamics, which of the following expressions correctly defines Net Primary Productivity (NPP)?